Python Cheatsheet


Click on the buttons to help you with particular Python skills


Variables

Printing / Output

String Functions

Input

Comparative Operators

If Statements / Selection

Iteration / Loops

Functions

Data Strcutres

List Functions

File Management

Miscalanious 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

  1. Variable names cannot take the name of a python reserved keyword such as print
  2. The name goes on the left ⬅ & the value goes on the right ➡
  3. Just use 1 =. Remember that == is a comparative operator.
  4. 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)
                        
0
1

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")
                
                  
    hi
    hi
    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)
                        
3

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)
                        
2

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)
                    
                        
    0
    1
    2

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)
                    
                        
    5
    6
    7

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
14
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?

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

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?

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

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

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']

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

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")

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

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())
                            
                        

                    

                

            


            

            

            
        

    

    

        
    




    

        
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))
                        

                    

                

                

                    

                       
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