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Python basics cheatsheet

Python Basics Cheatsheet

Python is an interpreted language.

Math, numbers and variables 

Mathematical Operators

Besides the usual operators (+, -, * and /), Python has exponent ( ** ) and negation ( - as a prefix to a number ).

Integers and Floats

Integers: 50
Floats: 3.1421

Order of operations

 PEMDAS: Parentheses, Exponent, Multiplication, Division, Addition and Subtraction

Using Variables

 No spaces in the variable name and must start with a character. Python style Pep 8 recommends lowercase words separated by underscore.


import math
math.ceil(4.8) // will print 5

Other python libraries


Create strings

first_name = ‘Aditya’
last_name = ‘Inapurapu’

Concatenate strings

full_name = first_name + ‘ ‘ + last_name

Print strings

// Print one string

// Print multiple strings one after the other with a space in between
print(first_name, last_name)

Python script

first_name = ‘Aditya’
last_name = ‘Inapurapu’
full_name = first_name + ‘ ‘ + last_name
print(first_name, last_name)

Execute the following shell command to execute the python script:


# is the comment character that makes the entire line in the python script as a comment.

Number to string

year = 1969
sentence = ‘The year was’ + str(year)
// A print statement automatically converts a number to a string
print(‘The year was’, year)

Single quotes in the string

famous_sketch = “Hell’s Grannies”

New line characters and tabs

famous_sketch1 = “\n\tHell’s Grannies”

String is an array of characters

greeting = ‘Hello World!’
#Prints H
#Prints !
#IndexError: string index out of range

Built-in String functions


greeting = ‘Hello World!’

Sliceword = ‘Python’

# Prints ‘tho’

Slice from the beginning of the string

word = ‘Good’
#Print from the beginning of the string to index 2
#Also prints from the beginning of the string to index 2

Slice from the middle to the end of the string

word = ‘Good’
#Print from index 2 to the end of the string

Halfway index of the string using Integer division

// - is the Integer division operator which divides and always returns a whole number
word1 = ‘Good’
half1 = len(word1)//2
end1 = word1[half1:]
word2 = ‘Evening’
half2 = len(word2)//2
end2 = word2[half2:]
print(end1, end2)



if num_knights < 3:
      print(‘Raise the white flag!’)
print (‘Knights of the Round Table!’)

if num_knights < 3:
elif num_knights >= 10:
      print(‘Trojan Rabbit’)


day = input(“Enter the day of the week”)
print(‘You entered:’, day)

Convert from string to int

num_knights = int(input(‘Enter the number of knights’))
print(‘You entered: ‘, num_knights)
if num_knights < 3 or day == ‘Monday’:

Nested if

if enemy == ‘Killer bunny’:
      print(‘Holy Hand Grenade!’)
if num_knights >= 10 and day == ‘Wednesday’
      print(‘Trojan Rabbit!’)

Core data structures


# An empty list
empty = []

# A list of numbers
nums = [1, 2, 3, 4]

# A list of strings
words = [‘word1’, ‘word2’, ‘word3’]

# A list of mixed items
anything = [10, ‘hello’, ‘ahoy’, ‘mate’, 123.45]
# Prints 10
# Prints ahoy
# Prints hello ahoy

# Append items to the list

# Remove item by value

# Remove item by index
del anything[0]

# Remove items by slice
del anything[1:3]


Dictionaries are equivalent to maps in Java where the data structure is a heap of key value pairs.
slang = {‘cheerio’: ‘goodbye’, ‘knackered’: ‘tired’, ‘yonks’: ‘ages’}
# Prints goodbye

# Empty dictionary
slang = {}

# Add key value pairs or update values
slang[‘knackered’] = ‘tired’
slang[‘smashing’] = ‘terrific’

# Delete items from the dictionary
del slang[‘cheerio’]

# If the key does not exist, a KeyError occurs and stops program execution. Use the get method to avoid this issue. If the key does not exist, ‘None’ will be returned.
result = slang.get(‘bloody’)
# if result exists
if result:
      print(‘Key does not exist’)

Comparing Lists

my_list = [1, 2, 3, 4]
your_list = [4, 3, 2, 1]
his_list = [1, 2, 3, 4]
# Not equals returns false
print(my_list == your_list)
# Equals returns true
print(my_list == his_list)

Comparing Dictionaries

my_dictionary = {1:1, 2:2, 3:3, 4:4}
your_dictionary = {4:4, 3:3, 2:2, 1:1}
# Equals returns true
print(my_dictionary == your_dictionary)

List of lists

menus = [[ ‘Spam n Eggs’, ‘Spam n Jam’, ‘Span n Ham’],
      [‘SLT (Spam-Lettuce-Tomato)’, ‘PB&S (PB&Spam)’],
      [‘Spalad’, ‘Spamghetti’, ‘Spam noodle soup’]]

Dictionary of lists

menus = {‘Breakfast’: [ ‘Spam n Eggs’, ‘Spam n Jam’, ‘Span n Ham’],
      ‘Lunch’: [‘SLT (Spam-Lettuce-Tomato)’, ‘PB&S (PB&Spam)’],
      ‘Dinner’: [‘Spalad’, ‘Spamghetti’, ‘Spam noodle soup’]}
print(‘Breakfast Menu:\t’, menus[‘Breakfast’])
print(‘Lunch Menu:\t’, menus[‘Lunch’])


For loop

prices = [2.50, 3.50, 4.50]
# Print all prices using a loop
for price in prices:
      print(‘Price is’, price)
total = 0
for price in prices:
      print(‘Price is’, price)
      total = total + price
      print(‘total is’, total)
average = total/len(prices)
print(‘Average is’, average)

Generate a random number

import random
# Generates a random number from [0.0, 1.0]
r1 = random.random()
# Generates a random choice from a list
r2 = random.choice([1, 2, 3, 4, 5])
# Generates a random number between 1 and 1000
r3 = random.randint(1, 1000)

Simple range function

# Creates a list containing numbers 0 to 9

for i in range(10):
      ticket = random.randint(1, 1000)

Start, Stop and Step range function

# Creates a list containing numbers ranging from 2005 to 2016 incrementing by 2
for i in range(2005, 2016, 2):
# The above prints 2005, 2007, 2009, 2011, 2013, 2015

More loops

# Append ‘spam’ to each word inside a list.
slang = [‘Knackered’, ‘Pip pip’, ‘Squidgy’, ‘Smashing’]
for word in slang:
      menu.append(word + ‘ Spam)
# Assign prices to each menu item in a dictionary.
menu = [‘Knackered Spam’, ‘Pip pip Spam’, ‘Squidgy Spam’, ‘Smashing Spam’]
menu_price = {}
price = 0.50
for item in menu
      menu_prices[item] = price
      price = price + 1

# Print the keys in the dictionary
for item in menu_prices:

# Print key value pairs
for name, price in menu_prices.items():
      print(name, ‘: $’, price)

# Print without extra spaces
print(name, ‘: $’, price, sep=’’)

# Round/Format to 2 decimal places
print(name, ‘: $’, format(price, ‘.2f’), sep=’’)

While loop

x = 1
while x != 3:
      print(‘x is’, x)
      x = x + 1

orders = []
order = input(“What would like to order? (Q for Quit)”)
while (order.upper() != ‘Q’)
      # Find the order and add it to the list if it exists
found = menu.get(order)
if found:
print(“Menu item doesn’t exist”)

# Check if the customer wants to order anything else
order = input(“Anything else? (Q to Quit)”)


while (True)
      if order.upper() == ‘Q’:


while (True)
      if order.upper() == ‘Q’:
      if order == ‘Cheeky Spam’:
           print(“Sorry, we’re all out of that!”)


Define a function

def average(prices):
return avg

Call a function

numbers = [1, 2, 3, 4, 5]
my_average = average(numbers)


Good practice to have a function name main.

def average(numbers):
      total = 0
      for num in list:
           total = total + num
      avg = total/len(numbers)
      return avg

def main():
prices = [29, 21, 55, 10]
result = average(prices)


Writing files

#Open the file in ‘w’ write mode
sales_log = open(‘spam_orders.txt’, ‘w’)
# If the file does not exist, python will create it for us.
sales_log.write(‘The Spam Van’)
sales_log.write(‘Sales log’)

# Append  mode
sales_log = open(‘spam_orders.txt’, ‘a’)

Reading files

# Read and print the entire file
dollar_spam = open(‘dollar_menu.txt’, ‘r’)

# Read one line at a time
dollar_spam = open(‘dollar_menu.txt’, ‘r’)
print(‘1st line:’, dollar_spam.readline())
print(‘2nd line:’, dollar_spam.readline())

# Read one line at a time in a loop till end of the file
dollar_spam = open(‘dollar_menu.txt’, ‘r’)
for line in dollar_spam:

# Read one line at a time into a list
dollar_spam = open(‘dollar_menu.txt’, ‘r’)
dollar_menu = []
for line in dollar_spam:

#Remove the leading and trailing new line character
dollar_spam = open(‘dollar_menu.txt’, ‘r’)
dollar_menu = []
for line in dollar_spam:
        line = line.strip()


Python has 60 plus exceptions.

Try, Except

      file = open(‘sales.txt’, ‘r’)
      print(“File doesn’t exist”)

Capture the error as a variable

price = float(price)
print(‘Price =’, price)
except ValueError as err:


Installing modules

pip install requests - for all available Python packages

JSON to format and share data

first_item = {‘name’: ‘Spam n Eggs’,
           ‘description’: ‘Two eggs with Spam’,
           ‘price’: 2.50}
second_item = {‘name’:’Span n Jam’,
‘description’:’Biscuit with Jam with Spam’,
‘price’: 3.50}
menu_items = [first_item, second_item]
print(menu_items[0][‘name], menu_items[0][‘price’], menu_items[0][‘desc’]

# Get JSON from a http request
import requests

my_request = requests.get(‘’)
menu_list = my_request.json()
print(“Today’s Menu:”)
for item in menu_list:
      print(item[‘name’], item[‘desc’], item[‘price’]

Create your own module

def print_menu(menu):

def get_order(menu):

def total_bill(orders, menu):

import orders

def main():
      menu = {‘Cheerio Spam”: 0.50, …}
      orders = orders.get_order(menu)
      total = orders.bill_total(orders, menu)
      print(‘You ordered:’, order, ‘Total:’ total)

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#Git starter cheat sheet

Initialize a local repo Run the following command in the folder where you would like to initialize a git repo.
git init
Get status It is a good practice to frequently run check on status during development. The following command points out the changes between the previous commit and current state of the folder.
git status
Add content To add an untracked file named ‘text.txt’ to the staging area, execute the following command.
git add text.txt
Syntax: git add <filename>
Commit changes To commit changes made to the folder, execute the following command. The message will be used as a commit message to associate this check-in with the message.
git commit –m “Add text.txt to the code base.”
Syntax: git commit –m “<Commit message>”
Add using wild card To add multiple files using a wild card character, execute the following command.
git add ‘*.txt’
Syntax: git add ‘<wildcard_character+string>’
Check history Review commit history using the following command.
git log
Add Remote re…