Python Cheatsheet

Click on the buttons to help you with particular Python skills

A big thanks goes out to my year 10,11 and 12 students who helped contribute by creating many of the modals on this page.

Variables

Printing / Output

String Functions

Input

Comparative Operators

If Statements / Selection

Iteration / Loops

Functions

Data Structures

List Functions

File Management

Functions for numbers

Miscellaneous skills

The cheatsheet is a work in progress. feel free to contribute. :-)

count

The .count() function will count how many times a certain value appears within a string.




  sentence = input("Enter your sentence: ")
  e_count = sentence.count("e")
  print("There are", e_count, "e's!")

Enter your sentence: Hello there

There are 3 e's!

Variables

There are some golden rules when assigning

Variable names cannot take the name of a python reserved keyword such as print
The name goes on the left ⬅ & the value goes on the right ➡
Just use 1 =. Remember that == is a comparative operator.
Variable names cannot have spaces.

score = 0
name = "codefez"

Re-assigning Variables

if you assign a value to a variable name that already exists, you will simply re-assign the original variable a new value.
This will result in losing the value that was originally held.

score = 0
print(score)

score = 1
print(score)

Multiple Variables ➡️ 1 line

Assigning variables can take up several lines! We can reduce the amount of required lines by assigning multiple variables on one line.

name, age, wears_glasses = "Joshua", 23, True
print(name, age, wears_glasses)

Joshua 23 True

Print

print() is a Python function for displaying text on the screen. Anything between the parenthesis is printed on the screen.

However! Python can only handle one datatype at a time. (see or for more info)
You can print any datatype.

print("Hello world!")
print(2+2) # calculates a result!

Hello World!
  4

Casting

Python can only handle one type of data at a time. Casting must be used in order to combine a second datatype.
str() converts data into a string datatype
int() converts data into a integer datatype
float() converts data into a real/float datatype

data_a = "Jessica"
data_b = 35
print(data_a + " is " + str(data_b) + " years old")

Jessica is 35 years old

For Loops

a for loop allows us to iterate a list of instructions for a specified number of times.

for i in range(3):
    print("hi")

The i represents a local variable.
Imagine that the i stands for iteration.

The i can be replaced by another name such as x or word or name.

The only rule here is to not name the local variable with a variable already used in your code or one that is a reservered word such as print or for.

for number in range(3):
    print(number)

  0
    1
    2

len()

The len() evaluates how big an object is.

In this case of a string, this is how many characters.

text = "fez"
len_of_text = len(text)
print(len_of_text)

In the case of a list, it is how many elements there are in the list.

myList = ["fez", "code"]
len_of_list = len(myList)
print(len_of_list)

The `range()` function

The range() function is often used in a for loop.
It specifies between which number of times the for instructions should repeat.

for i in range(3):
    print(i)

The range() function can also be given arguments specifying
the number to start and end the range count.

for i in range(5,8):
    print(i)

💡 The range also means that the local variable (eg. i) will be represent a number.

Python counts up until a number and not including! remember that zero is the first number.

number input()

The input() function can also be used to collect user responses as either integers or numbers with decimals.

once the input is collected from the user, it is then cast into either a integer or a float (a number with decimals).

# This is an input for whole number (integer)
age = int(input("Enter your age"))

# This is an input for a floating point
# number (with decimals)
shoe_size = float(input("Enter your shoe size"))

Enter your age

Enter your shoe size

8.5

input()

The input() function pauses when executing the line of code for the user to enter an input.

The input must be stored in a variable.

age = input("How old are you?\n>")

How old are you?

The default datatype for an input is a string. So anything that is saved in the variable after the input will be saved in quotes " "

In / Not In

The in operator checks if a character from a string or an element is in a list.

items = ["carrot","tomato","lettuce"]
if "tomato" in items:
    print("List includes fruit")
else:
    print("No fruit in list")

List includes fruit

The not in operators checks if a character from a string or an element is NOT in a list.

items = ["carrot","tomato","lettuce"]
if "tomato" not in items:
    print("No fruit in list")
else:
    print("fruit in list")

fruit in list

if / else

The if function selects code for execution if a condition is met. If it is not met, the instruction nested under the else block is executed.

x = 10

if x > 5:
    print("x is greater than 5")
else:
    print("x is less than or equal to 5")

x is greater than 5

elif

The elif operand will execute the block of code if a given condition is met and doesn't meet the first condition.



x = 2

if x > 5:
    print("x is greater than 5")
elif x > 2:
    print("x is greater than or equal to 2")
else:
    print("x is less than 2")

x is greater than or equal to 2

Ternary operators

Ternary operators allow you to execute an if/else statement on one line.




  x = int(input(" "))
  print("x is equal to 4.") if x==4 else print("x is not equal to 4")

Comments

The # symbol creates a line that is ignored by Python. This is called a comment and can be used to describe the purpose of a block of code for clarity later.

# The line below asks for a user's age
age = int(input("What's your age?"))

What's your age?

Multiple comment lines can also be achieved by using either 3 single or 3 double quotes

"""The line below asks 
for a user's age """
age = int(input("What's your age?"))

'''The line above asks 
for a user's age '''

What's your age?

Comment a line/s by highlighting it and hit the
ctrl + / keys.

lower / upper

The lower() function converts all alphanumeric characters into lowercase

name = "CodeFez"
print(name.lower())

codefez

The upper() function converts all alphanumeric characters into uppercase

name = "CodeFez"
print(name.upper())


                
                    
                        CODEFEZ




    
        
            
          
        while
        
            The while loop keeps running until a certain condition is met. 
            You can replace the printing and incrementing with any code you want.
        
                    
            

                
                    
                        # The counter can help escape a loop
counter = 1

while counter <= 5:
    print(counter)

    # Increment the counter 
    counter += 1
                        
                    
                
                
                    
                        1
    2
    3
    4
    5
                        
                    
                
            
            
        
    
        
            

                
                
                    If the counter is not outside of the while block, you may be stuck in a infinite loop.
                
            
          
    
    
      
    



    
        
            
        
        Open
        
            The open() function will take a filepath as an argument to open a file.
            

            There are 2 methods to opening a file. Both methods will assign the open file to a variable.
            

            Notice the 2 examples below have 2 arguments. The filename and then the access mode.
        
        
            

                
                    
                        # The open file is assigned to a variable
file = open("filename.txt", "r")

# Opened files should also be closed.
file.close()
                        
                    
                

                
                    
                        """ with this method, there is no need to 
close the file. """
with open("filename.txt", "r") as file:
    # add instructions here
                        
                    
                
                
            
            

        
        
        
            
            
                Files should be opened with an access mode. 
                
                    "r" is for opening a file only for reading it.
                    "w" is for overwriting all contents of the file.
                    "a" is for appending to a file.
                
            
        
                   
    
    
      
    



    
        
            
          
        read
        
            The read() function reads the contents of an opened file.
            The example is set up as if the file is called names.txt with 3 names.
        
        
        
            
                Alice

                Barbara

                Chelsea
            
        
        
        
            
            

                
                    
                        file = open("names.txt", "r")
data = file.readlines()
file.close()
print(data)
                        
                    
                
                
                    
                        ['Alice\n', 'Barbara\n', 'Chelsea']
                    
                
            
            
        
        
            
            As you can see, each username has a \n at the end of the name. We can remove that using the rstrip() method
           
        
        
            

                
                    
                        file = open("names.txt", "r")
data = file.readlines()
file.close()
print(data)

for name in range(0, len(data)):
    data[name] = data[name].rstrip("\n")
print(data)
                        
                    
                
                
                    
                        ['Alice\n', 'Barbara\n', 'Chelsea']
                        ['Alice', 'Barbara', 'Chelsea']
                    
                
            
        
    
    
      
    




  
    
      
    
    
    randint (from random)
    
    

      The random.randint(x,y) function will generate a random number from x to y.
    

    
    
      
    

      
        
          
            
import random
x=random.randint(3,7)
print(x)
print("This could be 3, 4, 5, 6 or 7.")
            
          
        
      
      
      
      
      
      
        
          
          6
          This could be 3, 4, 5, 6 or 7.
        
      
    
    
    

  
  
    
  



    
        
            
          
        Write
        
            The write() function writes a line to a file.
            
        
        
            Method 1

            

                
                    
                        with open("filename.txt", "a") as file:
    content = "A line of text.\n"
    file.write(content)
                        
                    
                
 

                Method 2

                
                    
                        file = open("filename.txt", "a")
content = "A line of text.\n"
file.write(content)
file.close()
                        
                    
                
            
            
        
                   
    
    
      
    



    
        
            
        
        quit
        
            The quit() function will end the program.
        
                
        
            
            

                
                    
                        print("Hello")
quit()
print("world")
                        
                    
                
                
                    
                        Hello
                    
                
            
            
        
                   
    
    
      
    



    
        
            
        
        Index
        
            The index() method will find the position of the first occurance of an item in a list.
            
Sometimes it's easier to find the position using a for loop and not the index method. See 2nd example.
        
                
        
            First Example 

            

                
                    
                        items = ["apple", "banana", "kiwi"]
pos = items.index("banana")
print(f"position of banana is {pos}.")
                        
                    
                
                
                    
                        position of banana is 1.
                    
                
            
            
        

        
            Second Example 

            

                
                    
                        items = ["apple", "banana", "kiwi"]
target = "banana"
for pos in range(0, len(items)):
    if target == fruit[pos]:
        print(f"position of {target} is {pos}.")
                        
                    
                
                
                    
                        position of banana is 1.
                    
                
            
            
        
                   
    
    
      
    



    
        
            
          
        split
        
            The split() method will seperate items in a string.
        
                
        
            
            

                
                    
                        string = "Superman,Clark Kent,can fly,super strength"
print(string)
name,alias,power1,power2 = split(",")
print(f"{name} is also known as {alias} and has the 
        powers {power1} and {power2}.")
                        
                    
                
                
                    
                        Superman,Clark Kent,can fly,super strength
                        Superman is also known as Clark Kent and has the powers can 
       fly and super strength.
                        
                    
                
            
            
        
                   
    
    
      
    



    
        
            
        
        Append
        
            The append() method is used to add data to a list.
            
        
        
            
            

                
                    
                        items = ["carrot","tomato"]
items.append("lettuce")
print(items)
                            
                        
                    
                
                
                                            
["carrot","tomato","lettuce"]
                    
                
            
        The new item has now been added to the list of items.  
        
                   
    
    
    
      
    



    
        
            
        
        Pop / Remove items
        
            The pop() method will remove an item from a list.
            
By default with no argument, it will remove the last time in the list.
            
With an argument, it will remove the index item of the number given.
        
                
        
            Without an argument
            

                
                    
                        veg = ["carrot","tomato","lettuce"]
veg.pop()
print(veg)
                        
                    
                
                
                    
                        ["carrot","tomato"]
                        
                    
                
            
            
        
         
        
        
            With an argument
            

                
                    
                        veg = ["carrot","tomato","lettuce"]
veg.pop(1)
print(veg)
                        
                    
                
                
                    
                        ["carrot","lettuce"]
                        
                    
                
            
            
        
    
    
      
    



    
        
            
          
        Round
        
            Rounding is used to display a numerical value to it's nearest integer.
            For example 5.3 can be rounded to 5 or 3.333333333333 can be rounded 

            to 3.33

            by default the round() method will 

            round to 2 decimal places unless specified.
        
                
        
            
            

                
                    
                        # Rounding to the nearest integer with no decimal places.
print(round(10/3,0)) 
# we can also use the int function to remove the decimal point.
print(int(round(10/3,0)))

# Rounding to 2 decimal places
print(round(10/3,2))
                        
                    
                
                
                    
                        3.0
                        3
                        3.33
                    
                
            
            
        
                   
    
    
      
    



    
        
            
        
        Basic Operators
        
            Python uses operators to perform mathematical operations.
        
                
        
            
            

                
                    
                        print(2+2) # Addition
print(3-2) # Subtraction
print(2*2) # Multiplication
print(5+2) # Division

                        
                    
                
                
                    
                        4
                        1
                        4
                        2.5
                    
                
            
            
        
                   
    
    
      
    



    
        
            
          
        Div / Mod
        
            To perform integer and remainder divisions, Python uses the div (//) and mod (%) operators.
        
                
        
            
            

                
                    
                        # integer division (//) only returns a whole number
print(5//2)

# Remainder division (%) returns the remainder of a division
print(5%2) # 2 remainders of 0.5 --> so 1 in total
print(4%2) # --> 0
print(11%3) # --> 2

                        
                    
                
                
                    
                        2

                        1
                        0
                        2
                    
                
            
            
        
                   
    
    
      
    



    
        
            
          
        Append
        
            f-strings are a simple way to concatenate strings, integers and other datatypes into a string of text. 

            Python automatically formats the datatype to string. 

            Curley brackets are used to interpolate variables into a string.
        
        
            
            

                
                    
                        name = "Alice"
age = 17
print(f"{name} was just {age} years old")
                        
                    
                
                
                    
Alice was just 17 years old
                    
                
            

        
        
            
            Check out the f-strings guide here.
                      
    
    
      
    






  
    
      
    
    
    sleep
    
    
    
      To be able to use sleep you need to from time import sleep. Then, using the function sleep(1), you can specify the amount of seconds within the parentheses ().
    
    
    
    
      
      

        
          
            
from time import sleep

sleep(1) # Waits 1 seconds
print("Hello")
sleep(1) # Waits 1 seconds
print("World")

            
          
        
      
        
        
        
        
          
          
            
            Hello
            World
        
      
      
    
  
  
    
  



    
        
            
          
        Tuples
        
            The tuple data structure is an immutable list which means they cannot be changed while the program is running.
        
        
                        
            

                
                    
                        
    animals = ("cat", "dog", "mouse") # defining the tuple 
    print(animals[0]) # prints the first item in the tuple from 0

    animals.append("rabbit")
                        

                    

                

                
                    
                        cat
                        AttributeError: 'tuple' object has no attribute 'append'
                    
                
            

            
        
                   
    

    
      
    




    
      
        
      
      
      input float
  
      
      
        The input() function can also be used a decimal integer. For example, inputting a number as a float and then printing it will print it as a decimal value.
      
  
      
      
  
      
      

        
          
              
  
  
    x = float(input("Enter a number"))
    print(x)
  
            
          
        
        
  
        
        
          
            
            Enter a number 51
       51.0
            
          
        
      
  
    
    
      
    
  

    
        
            
        
        islower() / isupper()
        
            The islower() and isupper() 
            string methods returns a True or False 
            result if all charcaters in a string are either all lower or uppercase.
            

        
        
            
            

                
                    
                        string1 = "HELLO WORLD"
string2 = "hello world"

print(string1.isupper())  # Output: True
print(string2.isupper())  # Output: False
                        
                    
                
                
                    
                        True
    >  False
                        
                    
                
            
            
        
                   
    
    
      
    






  
    
      
    
    
    Sorting Lists
    
    
    
      The sort() function will sort a list of numbers from an array in ascending order.
    

    
    
    
    
    

      
        
          

  numbers = [4, 2, 9, 1]
  numbers.sort()
  print(numbers)

          
        
      
      
      
      
      
        
          
          [1, 2, 4, 9]
        
      
    
    
    

  
  
    
  






  
    
      
  
    
    Clear Screen
    
    
    
      To clear the screen, you first need to import os then using os.system('clear') you will successfully clear it.
      For demonstration purposes, I have also used a sleep function which you can find in the cheatsheet also.
    

    
    
    
    
    

      
        
          
  import os
  from time import sleep
  
  print("Hello World") # Prints 'Hello World'
  sleep(1) # Waits for 1 second
  os.system('clear') # Clears screen

          
        
      
      
      
      
        
        
          Hello World
        
      
    
    
    

  
  
    
  




  
    
      
    
    
    Replace function
    
    
    
      The replace() function can be used to replace all occurrences of a specific substring within a string with a new substring.
    

    
    
    
    
    

      
        
          


  from time import sleep
  
  text = "Hello, World!"
  print(text) # Output: Hello World
  
  text.replace("World", "Hello")
  print(text) # Output: World Hello

          
        
      
      
      
      
      
        
          
            Hello World
            Hello Hello
        
      
    
    
    

  
  
    
  




  
    
      
    
    
    lists
    
    
    
      Lists are used to store multiple items in a single variable.
      Using square brackets[ ] with an assigned variable name allows us to create a list.
      Lists can contain all datatypes such as integer, boolean, string and float.
    

    
    
    
    
    

      
        
          


  mixed_list = [True, False, 'Hello', 'World', 1, 34, 2.4, 4.5]
  print(mixed_list)

          
        
      
      
      
      
      
        
          
          [True, False, 'Hello', 'World', 1, 34, 2.4, 4.5]
        
      
    
    
    

  
  
    
  



    
        
            
        
        Lost Modal
        
            This modal is lost. check back later to see if we've found it. 

        
        
            
        
        
            My people are working on this!
        
           
    
    
      
    


    
        
            
        
        isdigit()
        
            The isdigit() string method will check if a variable is numeric and return a 
            True or False result.
        

        
        
            
            

                
                    
                                                    
                            
var1 = "1"
var2 = "one"
print(var1.isdigit())
print(var2.isdigit())
                            
                        
                    
                
                

                
                
                    
                        
                        
                    
                
            

            

            

            
        
    
    
        
    


    
        
            
        
        isalpha()
        
            The isalpha() string method will check if a variable is alphanumeric and return a 
            True or False result.
        

        
        
            
            

                
                    
                                                    
                            
var1 = "1"
var2 = "one"
print(var1.isalpha())
print(var2.isalpha())
                            
                        
                    
                
                

                
                
                    
                        
                        
                    
                
            

            

            

            
        
    
    
        
    



    
        
            
        
        Random Choice
        
            The choice function chooses a random item from a list
        
        
                        
            

                
                    
                        from random import choice
numbers_list = [1, 2, 3, 4] 
print(choice(list))
                        

                    

                

                
                    
                       3
                        
                    
                
            

            
        
                   
    

    
      
    




    
      
        
      
      
      try and except
  
      
      
        A try-except block is used to handle exceptions, which are errors that occur 
        during the execution of a program. This block lets you manage these errors 
        gracefully without crashing your program.
      
      
        The try block contains the code that might raise an exception. 

        The except block contains the code to execute if an error occurs.
      
  
      
      
  
      
      

        
          
              
  
  
try:
    with open("users.txt", 'r') as file:
        content = file.read()
        # more code to do something with the file here
except FileNotFoundError:
    print(f"Error: The file '{users.txt}' was not found.")
  
            
          
        
        

        Another example
    
    
        
          
              
  
  
try:
    age = int(input("Enter your age: "))
    print(f"Great! You are {age} years old.")
except ValueError:
    print("Error: Please enter a valid number.")
  
            
          
        
        
  
        
        
          
            
            Enter your age:
            E3
            Error: Please enter a valid number.
          
        
      
      
      
  
    
    
      
    





  
    
  

sample (from random)


  The random.sample function will generate x random values from list.

 
    



  
    
      
import random
myList=[1,2,3,4,5,6,7,8,9,10]
x=random.sample(myList,3)
print(x)
print("These will be 3 numbers from 1-10, unordered.")

      
    
  

  
  
  
    
      
      [9,3,7]
      These will be 3 numbers from 1-10.
    

  
      



 
  






    
        
            
        
        Procedures
        
            The def keyword is used to define a function or procedure. 
 
            A procedure performs a task but doesn’t return a value.  

            Instead, it might print to the screen or modify a file.
        

        

            

                
                    
                                                    
def print_receipt(items, prices):
    print("Receipt:")
    for i in range(0, len(items)):
        print(f"{items[i]}: £{prices[i]}")
    print("Thank you for shopping.\nPlease come again!")

items = ["Apples", "Bananas", "Cherries"]
prices = [2.5, 1.2, 3.0]
print_receipt(items, prices)
                           
                        
                    
                
                
                    
                        Receipt:
Apples: £2.5
Bananas: £1.2
Cherries: £3.0
Thank you for shopping
Please come again!
                        
                                           
                
        
       
    
    
      
    



    
        
            
        
        Function
        
            The def keyword is used to define a function or procedure. 
 
            A function typically returns a value after performing a task.

            This functions takes a list of item prices and returns the total_price after working out the tax to be added.
        

        

            

                
                    
                                                    
def calculate_total_price(prices, tax_rate):
    total = sum(prices) * (1 + tax_rate)
    return total

prices = [10.0, 20.0, 30.0]  # List of item prices
tax_rate = 0.2 
total_price = calculate_total_price(prices, tax_rate)
print(f"The total price is: £{total_price:.2f}")
                           
                        
                    
                
                
                    
                        The total price is: £72.00
                        
                                           
                
        
       
    
    
      
    




  
    
      
    
    
    math.floor
    
    
    
      The math.floor function will round a decimal number down to the nearest integer.
    

    
    
    
    
    

      
        
          


  import math

  print(math.floor(1.7))
  print(math.floor(0.3))

          
        
      
      
      
      
      
        
          
          1
          0
        
      
    
    
    

  
  
    
  




  
    
      
    
    
    math.ceil
    
    
    
      The math.ceil function will round a decimal number up to the nearest integer.
    

    
    
    
    
    

      
        
          


  import math

  print(math.ceil(1.7))
  print(math.ceil(0.3))

          
        
      
      
      
      
      
        
          
          2
          1
        
      
    
    
    

  
  
    
  




  
    
      
    
    
    2D Arrays
    
    
    
      Lists are used to store multiple items in a single variable. A 2D array is when each item 
      in a list is another list which contains it's own items. 
    

    
    
    
    
    

      
        
          


grid = [
  ["x","o","x"],
  ["o","x","o"],
  ["x","o","x"]
]
for r in grid:
  print(r)

          
        
      
      
      
      
      
        
          
          ['x', 'o', 'x']
  ['o', 'x', 'o']
  ['x', 'o', 'x']
          
        
      
    
    
    

  
  
    
  



    
        
            
          
        Input Validation using while
        
            We can use while loops as a form of input validation. 
 
            For example, we can provide a list of possible answers that the user must use from in order to 

            progress further.
        
                    
            

                
                    
                        possible_answers = ["y","yes","n","no"]
answer = ""
print("Do you wear a fez?")
while answer.lower() not in possible_answers:
    answer = input("Enter a valid answer (Y,Yes,N,No)\n")
    
print("answer acknowledged")
                        
                    
                
                
                    
                            Do you wear a fez?
    nope
    Enter a valid answer (Y,Yes,N,No)
    yup
    Enter a valid answer (Y,Yes,N,No)
    Y
    answer acknowledged