Python
High-level, versatile programming language known for readability and simplicity
Lessons
- What is Python?
- Python Getting Started
- Python Syntax
- Python Comments
- Python Variables
- Python - Variable Names
- Python Variables - Assign Multiple Values
- Python - Output Variables
- Python Data Types
- Python Numbers
- Python Casting
- Python Strings
- Python - Slicing String
- Python - Modify Strings
- Python - String Concatenation
- Python - Format - Strings
- Python - Escape Characters
- python-String Methods
- Python Booleans
- Python Operators
- Python Lists
What is Python?
Python is a popular programming language. It was created by Guido van Rossum, and released in 1991.
It is used for:
- development (server-side),
- software development,
- mathematics,
- system scripting.
What can Python do?
- Python can be used on a server to create web applications.
- Python can be used alongside software to create workflows.
- Python can connect to database systems. It can also read and modify files.
-Python can be used to handle big data and perform complex mathematics.
- Python can be used for rapid prototyping, or for production-ready software development.
Why Python?
- Python works on different platforms (Windows, Mac, Linux, Raspberry Pi, etc).
- Python has a simple syntax similar to the English language.
- Python has syntax that allows developers to write programs with fewer lines than some other programming languages.
- Python runs on an interpreter system, meaning that code can be executed as soon as it is written. This means that prototyping can be very quick.
- Python can be treated in a procedural way, an object-oriented way or a functional way.
Good to know
-The most recent major version of Python is Python 3, which we shall be using in this tutorial. However, Python 2, although not being updated with -anything other than security updates, is still quite popular.
- In this tutorial Python will be written in a text editor. It is possible to write Python in an Integrated Development Environment, such as Thonny, Pycharm, Netbeans or Eclipse which are particularly useful when managing larger collections of Python files.
- Python Syntax compared to other programming languages
- Python was designed for readability, and has some similarities to the English language with influence from mathematics.
- Python uses new lines to complete a command, as opposed to other programming languages which often use semicolons or parentheses.
- Python relies on indentation, using whitespace, to define scope; such as the scope of loops, functions and classes. Other programming languages often use curly-brackets for this purpose.
Example:
print("Hello, World!")
Example Description:
Python Getting Started
Python Install
Many PCs and Macs will have python already installed.
To check if you have python installed on a Windows PC, search in the start bar for Python or run the following on the Command Line (cmd.exe)
C:\Users\Your Name>python --version
To check if you have python installed on a Linux or Mac, then on linux open the command line or on Mac open the Terminal and type:
python --version
If you find that you do not have Python installed on your computer, then you can download it for free from the following website: https://www.python.org/
Python Quickstart
Python is an interpreted programming language, this means that as a developer you write Python (.py) files in a text editor and then put those files into the python interpreter to be executed.
print("Hello, World!")
Simple as that. Save your file. Open your command line, navigate to the directory where you saved your file, and run:
C:\Users\Your Name>python hello.py
Let's write our first Python file, called hello.py, which can be done in any text editor:
Example:
no example
Example Description:
Python Syntax
Execute Python Syntax
As we learned in the previous page, Python syntax can be executed by writing directly in the Command Line:
>>> print("Hello, World!")
Hello, World!
Or by creating a python file on the server, using the .py file extension, and running it in the Command Line:
C:\Users\Your Name>python myfile.py
Python Indentation
Indentation refers to the spaces at the beginning of a code line.
Where in other programming languages the indentation in code is for readability only, the indentation in Python is very important.
Python uses indentation to indicate a block of code.
Example:
example 1 :
if 5 > 2:
print("Five is greater than two!")
example 2 :
Syntax Error:
if 5 > 2:
print("Five is greater than two!")
example 3 :
if 5 > 2:
print("Five is greater than two!")
if 5 > 2:
print("Five is greater than two!")
example 4:
Syntax Error:
if 5 > 2:
print("Five is greater than two!")
print("Five is greater than two!")
Example Description:
Python Comments
- Comments can be used to explain Python code.
- Comments can be used to make the code more readable.
- Comments can be used to prevent execution when testing code.
Creating a Comment by #
Multiline Comments
Python does not really have a syntax for multiline comments.
Example:
example 1 : #This is a comment
print("Hello, World!")
example 2 : #print("Hello, World!")
print("Cheers, Mate!")
example 3 : #This is a comment
#written in
#more than just one line
print("Hello, World!")
example 4 :
"""
This is a comment
written in
than just one line
"""
print("Hello, World!")
Example Description:
Python Variables
Variables
Variables are containers for storing data values.
Creating Variables
Python has no command for declaring a variable.
Get the Type
You can get the data type of a variable with the type() function.
Single or Double Quotes?
String variables can be declared either by using single or double quotes:
x = "John"
# is the same as
x = 'John'
Case-Sensitive
Variable names are case-sensitive.
a = 4
A = "Sally"
#A will not overwrite a
Example:
example 1: x = 5
y = "John"
print(x)
print(y)
example 2: x = 4 # x is of type int
x = "Sally" # x is now of type str
print(x)
example 3: x = str(3) # x will be '3'
y = int(3) # y will be 3
z = float(3) # z will be 3.0
example 4: x = 5
y = "John"
print(type(x))
print(type(y))
Example Description:
Python - Variable Names
Variable Names
A variable can have a short name (like x and y) or a more descriptive name (age, carname, total_volume).
Rules for Python variables:
- A variable name must start with a letter or the underscore character
- A variable name cannot start with a number
- A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )
- Variable names are case-sensitive (age, Age and AGE are three different variables)
- A variable name cannot be any of the Python keywords.
Multi Words Variable Names
Variable names with more than one word can be difficult to read.
There are several techniques you can use to make them more readable:
Camel Case
Each word, except the first, starts with a capital letter:
myVariableName = "John"
Pascal Case
Each word starts with a capital letter:
MyVariableName = "John"
Snake Case
Each word is separated by an underscore character:
my_variable_name = "John"
Example:
example 1:
myvar = "John"
my_var = "John"
_my_var = "John"
myVar = "John"
MYVAR = "John"
myvar2 = "John"
example 2:
2myvar = "John"
my-var = "John"
my var = "John"
Example Description:
Python Variables - Assign Multiple Values
Many Values to Multiple Variables
Example:
example 1 : x, y, z = "Orange", "Banana", "Cherry"
print(x)
print(y)
print(z)
example 2 : x = y = z = "Orange"
print(x)
print(y)
print(z
example 3:
fruits =["apple", "banana", "cherry"]
x, y, z = fruits
print(x)
print(y)
print(z)
Example Description:
Python - Output Variables
Output Variables
The Python print() function is often used to output variables.
x = "Python is awesome"
print(x)
Example:
example 1 :
x = "Python"
y = "is"
z = "awesome"
print(x, y, z)
example 2 :
x = "Python "
y = "is "
z = "awesome"
print(x + y + z)
example 3 :
x = 5
y = 10
print(x + y)
example 4:
x = 5
y = "John"
print(x + y)
example 5:
x = 5
y = "John"
print(x, y)
Example Description:
Python Data Types
Built-in Data Types
In programming, data type is an important concept.
Variables can store data of different types, and different types can do different things.
Python has the following data types built-in by default, in these categories:
Text Type: str
Numeric Types: int, float, complex
Sequence Types: list, tuple, range
Mapping Type: dict
Set Types: set, frozenset
Boolean Type: bool
Binary Types: bytes, bytearray, memoryview
None Type: NoneType
Getting the Data Type
You can get the data type of any object by using the type() function:
--------------------------------------------------------------------------------
Setting the Data Type
In Python, the data type is set when you assign a value to a variable:
Example data type
x = "Hello World" str
x = 20 int
x = 20.5 float
x = 1j complex
x = ["apple", "banana", "cherry"] list
x = ("apple", "banana", "cherry") tuple
x = range(6) range
x = {"name" : "John", "age" : 36} dict
x = {"apple", "banana", "cherry"} set
x = frozenset({"apple", "banana", "cherry"}) frozenset
x = True bool
x = b"Hello" bytes
x = bytearray(5) bytearray
x = memoryview(bytes(5)) memoryview
x = None NoneType
--------------------------------------------------------------------------------------------------------------
Setting the Specific Data Type
If you want to specify the data type, you can use the following constructor functions:
example data type
x = str("Hello World") str
x = int(20) int
x = float(20.5) float
x = complex(1j) complex
x = list(("apple", "banana", "cherry")) list
x = tuple(("apple", "banana", "cherry")) tuple
x = range(6) range
x = dict(name="John", age=36) dict
x = set(("apple", "banana", "cherry")) set
x = frozenset(("apple", "banana", "cherry")) frozenset
x = bool(5) bool
x = bytes(5) bytes
x = bytearray(5) bytearray
x = memoryview(bytes(5)) memoryview
Example:
x = 5
print(type(x))
Example Description:
Python Numbers
Python Numbers
There are three numeric types in Python:
int
float
complex
Variables of numeric types are created when you assign a value to them:
x = 1 # int
y = 2.8 # float
z = 1j # complex
To verify the type of any object in Python, use the type() function:
Example
print(type(x))
print(type(y))
print(type(z))
------------------------------------------------------------------------------------
Int
Int, or integer, is a whole number, positive or negative, without decimals, of unlimited length.
Example
Integers:
x = 1
y = 35656222554887711
z = -3255522
print(type(x))
print(type(y))
print(type(z))
------------------------------------------------------------------------------------
Float
Float, or "floating point number" is a number, positive or negative, containing one or more decimals.
Example
Floats:
x = 1.10
y = 1.0
z = -35.59
print(type(x))
print(type(y))
print(type(z))
Float can also be scientific numbers with an "e" to indicate the power of 10.
Example
Floats:
x = 35e3
y = 12E4
z = -87.7e100
print(type(x))
print(type(y))
print(type(z))
------------------------------------------------------------------------------------
Complex
Complex numbers are written with a "j" as the imaginary part:
Example
Complex:
x = 3+5j
y = 5j
z = -5j
print(type(x))
print(type(y))
print(type(z))
-------------------------------------------------------------------------------
Random Number
Python does not have a random() function to make a random number, but Python has a built-in module called random that can be used to make random numbers:
Example
Import the random module, and display a random number from 1 to 9:
import random
print(random.randrange(1, 10))
Example:
x = 1 # int
y = 2.8 # float
z = 1j # complex
#convert from int to float:
a = float(x)
#convert from float to int:
b = int(y)
#convert from int to complex:
c = complex(x)
print(a)
print(b)
print(c)
print(type(a))
print(type(b))
print(type(c))
Example Description:
Python Casting
Specify a Variable Type
There may be times when you want to specify a type on to a variable. This can be done with casting. Python is an object-orientated language, and as such it uses classes to define data types, including its primitive types.
Casting in python is therefore done using constructor functions:
- int() - constructs an integer number from an integer literal, a float literal (by removing all decimals), or a string literal (providing the string represents a whole number)
- float() - constructs a float number from an integer literal, a float literal or a string literal (providing the string represents a float or an integer)
- str() - constructs a string from a wide variety of data types, including strings, integer literals and float literals
Example:
example 1:
x = int(1) # x will be 1
y = int(2.8) # y will be 2
z = int("3") # z will be 3
-----------------------------------
example 2:
x = float(1) # x will be 1.0
y = float(2.8) # y will be 2.8
z = float("3") # z will be 3.0
w = float("4.2") # w will be 4.2
-----------------------------------
example 3:
x = str("s1") # x will be 's1'
y = str(2) # y will be '2'
z = str(3.0) # z will be '3.0'
Example Description:
Python Strings
Strings
Strings in python are surrounded by either single quotation marks, or double quotation marks.
'hello' is the same as "hello".
You can display a string literal with the print() function:
example:
print("Hello")
print('Hello')
----------------------------------------------------------------------------
Quotes Inside Quotes
You can use quotes inside a string, as long as they don't match the quotes surrounding the string:
Example
print("It's alright")
print("He is called 'Johnny'")
print('He is called "Johnny"')
----------------------------------------------------------------------------
Assign String to a Variable
Assigning a string to a variable is done with the variable name followed by an equal sign and the string:
Example
a = "Hello"
print(a)
----------------------------------------------------------------------------
Multiline Strings
You can assign a multiline string to a variable by using three quotes:
Example
You can use three double quotes:
a = """Lorem ipsum dolor sit amet,
consectetur adipiscing elit,
sed do eiusmod tempor incididunt
ut labore et dolore magna aliqua."""
print(a)
-------------------------------------------------------------
Or three single quotes:
Example
a = '''Lorem ipsum dolor sit amet,
consectetur adipiscing elit,
sed do eiusmod tempor incididunt
ut labore et dolore magna aliqua.'''
print(a)
----------------------------------------------------------------
Strings are Arrays
Like many other popular programming languages, strings in Python are arrays of bytes representing unicode characters.
However, Python does not have a character data type, a single character is simply a string with a length of 1.
Square brackets can be used to access elements of the string.
Example
Get the character at position 1 (remember that the first character has the position 0):
a = "Hello, World!"
print(a[1])
-------------------------------------------------------------------
Looping Through a String
Since strings are arrays, we can loop through the characters in a string, with a for loop.
Example
Loop through the letters in the word "banana":
for x in "banana":
print(x)
---------------------------------------------------------------------------------
String Length
To get the length of a string, use the len() function.
Example
The len() function returns the length of a string:
a = "Hello, World!"
print(len(a))
-------------------------------------------------------------------------------
Check String
To check if a certain phrase or character is present in a string, we can use the keyword in.
Example
Check if "free" is present in the following text:
txt = "The best things in life are free!"
print("free" in txt)
Use it in an if statement:
Example
Print only if "free" is present:
txt = "The best things in life are free!"
if "free" in txt:
print("Yes, 'free' is present.")
--------------------------------------------------------------------------------
Check if NOT
To check if a certain phrase or character is NOT present in a string, we can use the keyword not in.
Example
Check if "expensive" is NOT present in the following text:
txt = "The best things in life are free!"
print("expensive" not in txt)
Use it in an if statement:
Example
print only if "expensive" is NOT present:
txt = "The best things in life are free!"
if "expensive" not in txt:
print("No, 'expensive' is NOT present."
Example:
Note: in the result, the line breaks are inserted at the same position as in the code.
Example Description:
Python - Slicing String
Slicing
You can return a range of characters by using the slice syntax.
Specify the start index and the end index, separated by a colon, to return a part of the string.
Get the characters from position 2 to position 5 (not included):
b = "Hello, World!"
print(b[2:5])
Note: The first character has index 0.
----------------------------------------------------------------------------------------------------
Slice From the Start
By leaving out the start index, the range will start at the first character:
Example
Get the characters from the start to position 5 (not included):
b = "Hello, World!"
print(b[:5])
----------------------------------------------------------------------------------------------------
Slice To the End
By leaving out the end index, the range will go to the end:
Example
Get the characters from position 2, and all the way to the end:
b = "Hello, World!"
print(b[2:])
----------------------------------------------------------------------------------------------------
Negative Indexing
Use negative indexes to start the slice from the end of the string:
Example
Get the characters:
From: "o" in "World!" (position -5)
To, but not included: "d" in "World!" (position -2):
b = "Hello, World!"
print(b[-5:-2])
Example:
-
Example Description:
Python - Modify Strings
Python has a set of built-in methods that you can use on strings.
------------------------------------------------------------------
Upper Case
The upper() method returns the string in upper case:
a = "Hello, World!"
print(a.upper())
------------------------------------------------------------------
Lower Case
Example
The lower() method returns the string in lower case:
a = "Hello, World!"
print(a.lower())
------------------------------------------------------------------
Remove Whitespace
Whitespace is the space before and/or after the actual text, and very often you want to remove this space.
Example
The strip() method removes any whitespace from the beginning or the end:
a = " Hello, World! "
print(a.strip()) # returns "Hello, World!"
------------------------------------------------------------------
Replace String
Example
The replace() method replaces a string with another string:
a = "Hello, World!"
print(a.replace("H", "J"))
------------------------------------------------------------------
Split String
The split() method returns a list where the text between the specified separator becomes the list items.
Example
The split() method splits the string into substrings if it finds instances of the separator:
a = "Hello, World!"
print(a.split(",")) # returns ['Hello', ' World!']
Example:
-
Example Description:
Python - String Concatenation
String Concatenation
To concatenate, or combine, two strings you can use the + operator.
Merge variable a with variable b into variable c:
a = "Hello"
b = "World"
c = a + b
print(c)
-----------------------------------------------------
Example
To add a space between them, add a " ":
a = "Hello"
b = "World"
c = a + " " + b
print(c)
Example:
-
Example Description:
Python - Format - Strings
String Format
As we learned in the Python Variables chapter, we cannot combine strings and numbers like this:
age = 36
txt = "My name is John, I am " + age
print(txt)
--------------------------------------------------------------------
But we can combine strings and numbers by using f-strings or the format() method!
F-Strings
F-String was introduced in Python 3.6, and is now the preferred way of formatting strings.
To specify a string as an f-string, simply put an f in front of the string literal, and add curly brackets {} as placeholders for variables and other operations.
Example
Create an f-string:
age = 36
txt = f"My name is John, I am {age}"
print(txt)
--------------------------------------------------------------------
Placeholders and Modifiers
A placeholder can contain variables, operations, functions, and modifiers to format the value.
Example
Add a placeholder for the price variable:
price = 59
txt = f"The price is {price} dollars"
print(txt)
--------------------------------------------------------------------
A placeholder can include a modifier to format the value.
A modifier is included by adding a colon : followed by a legal formatting type, like .2f which means fixed point number with 2 decimals:
Example
Display the price with 2 decimals:
price = 59
txt = f"The price is {price:.2f} dollars"
print(txt)
--------------------------------------------------------------------
A placeholder can contain Python code, like math operations:
Example
Perform a math operation in the placeholder, and return the result:
txt = f"The price is {20 * 59} dollars"
print(txt)
Example:
-
Example Description:
Python - Escape Characters
Escape Character
To insert characters that are illegal in a string, use an escape character.
An escape character is a backslash \ followed by the character you want to insert.
An example of an illegal character is a double quote inside a string that is surrounded by double quotes:
----------------------------------------------------------------------------------
Escape Characters
Other escape characters used in Python:
Code Result
\' Single Quote
\\ Backslash
\n New Line
\r Carriage Return
\t Tab
\b Backspace
\f Form Feed
\ooo Octal value
\xhh Hex value
Example:
example 1:txt = "We are the so-called "Vikings" from the north."
-----------------------------------------------
example 2 :txt = "We are the so-called \"Vikings\" from the north."
Example Description:
python-String Methods
String Methods
Python has a set of built-in methods that you can use on strings.
--------------------------------------------------------------------------------
Note: All string methods return new values. They do not change the original string.
Method ................................................... Description
capitalize() ................................................... Converts the first character to upper case
casefold() ................................................... Converts string into lower case
center() ................................................... Returns a centered string
count() ................................................... Returns the number of times a specified value occurs in a string
encode()................................................... Returns an encoded version of the string
endswith()................................................... Returns true if the string ends with the specified value
expandtabs()................................................... Sets the tab size of the string
find()................................................... Searches the string for a specified value and returns the position of where it was found
format()................................................... Formats specified values in a string
format_map()................................................... Formats specified values in a string
index() ................................................... Searches the string for a specified value and returns the position of where it was found
isalnum()................................................... Returns True if all characters in the string are alphanumeric
isalpha()................................................... Returns True if all characters in the string are in the alphabet
isascii()................................................... Returns True if all characters in the string are ascii characters
isdecimal()................................................... Returns True if all characters in the string are decimals
isdigit() ................................................... Returns True if all characters in the string are digits
isidentifier()................................................... Returns True if the string is an identifier
islower() ................................................... Returns True if all characters in the string are lower case
isnumeric()................................................... Returns True if all characters in the string are numeric
isprintable()................................................... Returns True if all characters in the string are printable
isspace()................................................... Returns True if all characters in the string are whitespaces
istitle()................................................... Returns True if the string follows the rules of a title
isupper()................................................... Returns True if all characters in the string are upper case
join()................................................... Joins the elements of an iterable to the end of the string
ljust() ................................................... Returns a left justified version of the string
lower() ................................................... Converts a string into lower case
lstrip() ................................................... Returns a left trim version of the string
maketrans()................................................... Returns a translation table to be used in translations
partition() ................................................... Returns a tuple where the string is parted into three parts
replace() ................................................... Returns a string where a specified value is replaced with a specified value
rfind() ................................................... Searches the string for a specified value and returns the last position of where it was found
rindex() ................................................... Searches the string for a specified value and returns the last position of where it was found
rjust() ................................................... Returns a right justified version of the string
rpartition() ................................................... Returns a tuple where the string is parted into three parts
rsplit() ................................................... Splits the string at the specified separator, and returns a list
rstrip()................................................... Returns a right trim version of the string
split() ................................................... Splits the string at the specified separator, and returns a list
splitlines() ................................................... Splits the string at line breaks and returns a list
startswith()................................................... Returns true if the string starts with the specified value
strip()................................................... Returns a trimmed version of the string
swapcase() ................................................... Swaps cases, lower case becomes upper case and vice versa
title() ................................................... Converts the first character of each word to upper case
translate()................................................... Returns a translated string
upper()................................................... Converts a string into upper case
zfill()................................................... Fills the string with a specified number of 0 values at the beginning
Example:
-
Example Description:
Python Booleans
Booleans represent one of two values: True or False.
Boolean Values
In programming you often need to know if an expression is True or False.
You can evaluate any expression in Python, and get one of two answers, True or False.
When you compare two values, the expression is evaluated and Python returns the Boolean answer:
print(10 > 9)
print(10 == 9)
print(10 < 9)
-----------------------------------------------------------------
When you run a condition in an if statement, Python returns True or False:
Example
Print a message based on whether the condition is True or False:
a = 200
b = 33
if b > a:
print("b is greater than a")
else:
print("b is not greater than a")
-----------------------------------------------------------------
Evaluate Values and Variables
The bool() function allows you to evaluate any value, and give you True or False in return,
Example
Evaluate a string and a number:
print(bool("Hello"))
print(bool(15))
-----------------------------------------------------------------
Example
Evaluate two variables:
x = "Hello"
y = 15
print(bool(x))
print(bool(y))
-----------------------------------------------------------------
Most Values are True
Almost any value is evaluated to True if it has some sort of content.
Any string is True, except empty strings.
Any number is True, except 0.
Any list, tuple, set, and dictionary are True, except empty ones.
Example
The following will return True:
bool("abc")
bool(123)
bool(["apple", "cherry", "banana"])
-----------------------------------------------------------------
Some Values are False
In fact, there are not many values that evaluate to False, except empty values, such as (), [], {}, "", the number 0, and the value None. And of course the value False evaluates to False.
Example
The following will return False:
bool(False)
bool(None)
bool(0)
bool("")
bool(())
bool([])
bool({})
-----------------------------------------------------------------
One more value, or object in this case, evaluates to False, and that is if you have an object that is made from a class with a __len__ function that returns 0 or False:
Example
class myclass():
def __len__(self):
return 0
myobj = myclass()
print(bool(myobj))
-----------------------------------------------------------------
Functions can Return a Boolean
You can create functions that returns a Boolean Value:
Example
Print the answer of a function:
def myFunction() :
return True
print(myFunction())
-----------------------------------------------------------------
You can execute code based on the Boolean answer of a function:
Example
Print "YES!" if the function returns True, otherwise print "NO!":
def myFunction() :
return True
if myFunction():
print("YES!")
else:
print("NO!")
-----------------------------------------------------------------
Python also has many built-in functions that return a boolean value, like the isinstance() function, which can be used to determine if an object is of a certain data type:
Example
Check if an object is an integer or not:
x = 200
print(isinstance(x, int))
Example:
print(10 > 9)
print(10 == 9)
print(10 < 9)
Example Description:
Python Operators
Python Operators
Operators are used to perform operations on variables and values.
In the example below, we use the + operator to add together two values:
print(10 + 5)
-------------------------------------------------------------------
Python divides the operators in the following groups:
- Arithmetic operators
- Assignment operators
- Comparison operators
- Logical operators
- Identity operators
- Membership operators
- Bitwise operators
-----------------------------------------------------------
Python Arithmetic Operators
Arithmetic operators are used with numeric values to perform common mathematical operations:
Operator Name .................................................... Example
+ .................................................... Addition x + y
- ....................................................Subtraction x - y
* .................................................... Multiplication x * y
/ ....................................................Division x / y
% ....................................................Modulus x % y
** ....................................................Exponentiation x ** y
// ....................................................Floor division x // y
-----------------------------------------------------------------
Python Assignment Operators
Assignment operators are used to assign values to variables:
Operator Example Same As
= ............................ x = 5 ................ x = 5
+= ........................... x += 3 .................. x = x + 3
-= ................ x -= 3 ................ x = x - 3
*= ................ x *= 3 ............... x = x * 3
/= ................ x /= 3 ................ x = x / 3
%= ................ x %= 3 ................ x = x % 3
//= ................ x //= 3 ................ x = x // 3
**= ................ x **= 3 ................ x = x ** 3
&= ................ x &= 3 ................ = x & 3
|= ................ x |= 3 ................ x = x | 3
^= ................ x ^= 3 ................ x = x ^ 3
>>= ................ x >>= 3 ................ x = x >> 3
<<= ................ x <<= 3 ................ x = x << 3
:= ................ print(x := 3) ................ x = 3print(x)
------------------------------------------
Python Assignment Operators
Assignment operators are used to assign values to variables:
Operator....... Example ............Same As
= x = 5 x = 5
+= .........x += 3 .........x = x + 3
-= .....x -= 3 .......x = x - 3
*= .........x *= 3 .......x = x * 3
/= x /= ..... ........x = x / 3
%= .......x %= 3 ...........x = x % 3
//= .....x //= 3 .......x = x // 3
**=....... x **= 3...... x = x ** 3
&= x &= 3 x = x & 3
|= x |= 3 x = x | 3
^= x ^= 3 x = x ^ 3
>>= x >>= 3 x = x >> 3
<<= x <<= 3 x = x << 3
:= print(x := 3) x = 3
print(x)
---------------------------------------------------------
Python Comparison Operators
Comparison operators are used to compare two values:
Operator Name Example Try it
== Equal x == y
!= Not equal x != y
> Greater than x > y
< Less than x < y
>= Greater than or equal to x >= y
<= Less than or equal to x <= y
---------------------------------------------------------------
Python Logical Operators
Logical operators are used to combine conditional statements:
Operator Description Example
and Returns True if both statements are true x < 5 and x < 10
or Returns True if one of the statements is true x < 5 or x < 4
not Reverse the result, returns False if the result is true not(x < 5 and x < 10)
Python Identity Operators
Identity operators are used to compare the objects, not if they are equal, but if they are actually the same object, with the same memory location:
Operator Description Example
is Returns True if both variables are the same object x is y
is not Returns True if both variables are not the same object x is not y
Python Membership Operators
Membership operators are used to test if a sequence is presented in an object:
Operator Description Example Try it
in Returns True if a sequence with the specified value is present in the object x in y
not in Returns True if a sequence with the specified value is not present in the object x not in y
Python Bitwise Operators
Bitwise operators are used to compare (binary) numbers:
Operator Name Description Example Try it
& AND Sets each bit to 1 if both bits are 1 x & y
| OR Sets each bit to 1 if one of two bits is 1 x | y
^ XOR Sets each bit to 1 if only one of two bits is 1 x ^ y
~ NOT Inverts all the bits ~x
<< Zero fill left shift Shift left by pushing zeros in from the right and let the leftmost bits fall off x << 2
>> Signed right shift Shift right by pushing copies of the leftmost bit in from the left, and let the rightmost bits fall off x >> 2
--------------------------------------------------------------
Operator Precedence
Operator precedence describes the order in which operations are performed.
Example
Parentheses has the highest precedence, meaning that expressions inside parentheses must be evaluated first:
print((6 + 3) - (6 + 3))
--------------------------------------------------
Example
Multiplication * has higher precedence than addition +, and therefore multiplications are evaluated before additions:
print(100 + 5 * 3)
--------------------------------------------------------
The precedence order is described in the table below, starting with the highest precedence at the top:
Operator Description
() Parentheses
** Exponentiation
+x -x ~x Unary plus, unary minus, and bitwise NOT
* / // % Multiplication, division, floor division, and modulus
+ - Addition and subtraction
<< >> Bitwise left and right shifts
& Bitwise AND
^ Bitwise XOR
| Bitwise OR
== != > >= < <= is is not in not in Comparisons, identity, and membership operators
not Logical NOT
and AND
or OR
------------------------------------------------------------
If two operators have the same precedence, the expression is evaluated from left to right.
Example
Addition + and subtraction - has the same precedence, and therefore we evaluate the expression from left to right:
print(5 + 4 - 7 + 3)
Example:
-
Example Description:
Python Lists
mylist = ["apple", "banana", "cherry"]
List
Lists are used to store multiple items in a single variable.
Lists are one of 4 built-in data types in Python used to store collections of data, the other 3 are Tuple, Set, and Dictionary, all with different qualities and usage.
Lists are created using square brackets:
Create a List:
thislist = ["apple", "banana", "cherry"]
print(thislist)
-------------------------------------------------------------
List Items
List items are ordered, changeable, and allow duplicate values.
List items are indexed, the first item has index [0], the second item has index [1] etc.
Ordered
When we say that lists are ordered, it means that the items have a defined order, and that order will not change.
If you add new items to a list, the new items will be placed at the end of the list.
-------------------------------------------------------------
Note: There are some list methods that will change the order, but in general: the order of the items will not change.
-------------------------------------------------------------
Changeable
The list is changeable, meaning that we can change, add, and remove items in a list after it has been created.
Allow Duplicates
Since lists are indexed, lists can have items with the same value:
Example
Lists allow duplicate values:
thislist = ["apple", "banana", "cherry", "apple", "cherry"]
print(thislist)
-------------------------------------------------------------
List Length
To determine how many items a list has, use the len() function:
Example
Print the number of items in the list:
thislist = ["apple", "banana", "cherry"]
print(len(thislist))
-------------------------------------------------------------
List Items - Data Types
List items can be of any data type:
Example
String, int and boolean data types:
list1 = ["apple", "banana", "cherry"]
list2 = [1, 5, 7, 9, 3]
list3 = [True, False, False]
-------------------------------------------------------------
A list can contain different data types:
Example
A list with strings, integers and boolean values:
list1 = ["abc", 34, True, 40, "male"]
type()
-------------------------------------------------------------
From Python's perspective, lists are defined as objects with the data type 'list':
<class 'list'>
Example
What is the data type of a list?
mylist = ["apple", "banana", "cherry"]
print(type(mylist))
-------------------------------------------------------------
The list() Constructor
It is also possible to use the list() constructor when creating a new list.
Example
Using the list() constructor to make a List:
thislist = list(("apple", "banana", "cherry")) # note the double round-brackets
print(thislist)
-------------------------------------------------------------
Python Collections (Arrays)
There are four collection data types in the Python programming language:
List is a collection which is ordered and changeable. Allows duplicate members.
Tuple is a collection which is ordered and unchangeable. Allows duplicate members.
Set is a collection which is unordered, unchangeable*, and unindexed. No duplicate members.
Dictionary is a collection which is ordered** and changeable. No duplicate members.
Example:
mylist = ["apple", "banana", "cherry"]
Example Description: