Python Cheat Sheet Mosh Hamedani, Apuntes de Programación Informática

¡Descarga Python Cheat Sheet Mosh Hamedani y más Apuntes en PDF de Programación Informática solo en Docsity!

Python

Cheat Sheet

Mosh Hamedani

Code with Mosh (codewithmosh.com)

1st Edition

About this Cheat Sheet

This cheat sheet includes the materials I’ve covered in my Python tutorial for

Beginners on YouTube. Both the YouTube tutorial and this cheat cover the core

language constructs but they are not complete by any means.

If you want to learn everything Python has to offer and become a Python expert,

check out my Complete Python Programming Course:

http://bit.ly/complete-python-course

• Variables
• Comments
• Receiving Input
• Strings
• Arithmetic Operations
• If Statements
• Comparison operators
• While loops
• For loops
• Lists
• Tuples
• Dictionaries
• Functions
• Exceptions
• Classes
• Inheritance
• Modules
• Packages
• Python Standard Library
• Pypi
• Want to Become a Python Expert?

Variables

We use variables to temporarily store data in computer’s memory.

price = 10 rating = 4. course_name = ‘Python for Beginners’ is_published = True

In the above example,

• price is an integer (a whole number without a decimal point)
• rating is a float (a number with a decimal point)
• course_name is a string (a sequence of characters)
• is_published is a boolean. Boolean values can be True or False. Comments

We use comments to add notes to our code. Good comments explain the hows and

whys, not what the code does. That should be reflected in the code itself. Use

comments to add reminders to yourself or other developers, or also explain your

assumptions and the reasons you’ve written code in a certain way.

This is a comment and it won’t get executed.

Our comments can be multiple lines.

Receiving Input

We can receive input from the user by calling the input() function.

birth_year = int(input(‘Birth year: ‘))

The input() function always returns data as a string. So, we’re converting the

result into an integer by calling the built-in int() function.

To check if a string contains a character (or a sequence of characters), we use the in

operator:

contains = ‘Python’ in course Arithmetic Operations

/ # returns a float // # returns an int % # returns the remainder of division ** # exponentiation - x ** y = x to the power of y

Augmented assignment operator:

x = x + 10 x += 10

Operator precedence:

1. parenthesis

2. exponentiation

3. multiplication / division

4. addition / subtraction

If Statements if is_hot: print(“hot day”) elif is_cold: print(“cold day”) else: print(“beautiful day”)

Logical operators:

if has_high_income and has_good_credit: ... if has_high_income or has_good_credit: ... is_day = True is_night = not is_day Comparison operators a > b a >= b (greater than or equal to) a < b a <= b a == b (equals) a != b (not equals) While loops i = 1 while i < 5 : print(i) i += 1

Dictionaries

We use dictionaries to store key/value pairs.

customer = { “name”: “John Smith”, “age”: 30 , “is_verified”: True }

We can use strings or numbers to define keys. They should be unique. We can use

any types for the values.

customer[“name”] # returns “John Smith” customer[“type”] # throws an error customer.get(“type”, “silver”) # returns “silver” customer[“name”] = “new name” Functions

We use functions to break up our code into small chunks. These chunks are easier

to read, understand and maintain. If there are bugs, it’s easier to find bugs in a

small chunk than the entire program. We can also re-use these chunks.

def greet_user(name): print(f”Hi {name}”) greet_user(“John”)

Parameters are placeholders for the data we can pass to functions. Arguments

are the actual values we pass.

We have two types of arguments:

• Positional arguments: their position (order) matters
• Keyword arguments: position doesn’t matter - we prefix them with the parameter

name.

Two positional arguments

greet_user(“John”, “Smith”)

Keyword arguments

calculate_total(order= 50 , shipping= 5 , tax=0.1)

Our functions can return values. If we don’t use the return statement, by default

None is returned. None is an object that represents the absence of a value.

def square(number): return number * number result = square(2) print(result) # prints 4 Exceptions

Exceptions are errors that crash our programs. They often happen because of bad

input or programming errors. It’s our job to anticipate and handle these exceptions

to prevent our programs from cashing.

try: age = int(input(‘Age: ‘)) income = 20000 risk = income / age print(age) except ValueError: print(‘Not a valid number’) except ZeroDivisionError: print(‘Age cannot be 0’) Classes

We use classes to define new types.

class Point: def init(self, x, y): self.x = x self.y = y def move(self): print(“move”)

importing the entire converters module

import converters converters.kg_to_lbs(5)

importing one function in the converters module

from converters import kg_to_lbs kg_to_lbs(5) Packages

A package is a directory with init.py in it. It can contain one or more

modules.

importing the entire sales module

from ecommerce import sales sales.calc_shipping()

importing one function in the sales module

from ecommerce.sales import calc_shipping calc_shipping() Python Standard Library

Python comes with a huge library of modules for performing common tasks such as

sending emails, working with date/time, generating random values, etc.

Random Module import random random.random() # returns a float between 0 to 1 random.randint(1, 6 ) # returns an int between 1 to 6 members = [‘John’, ‘Bob’, ‘Mary’] leader = random.choice(members) # randomly picks an item

Pypi

Python Package Index (pypi.org) is a directory of Python packages published by

Python developers around the world. We use pip to install or uninstall these

packages.

pip install openpyxl pip uninstall openpyxl Want to Become a Python Expert?

If you’re serious about learning Python and getting a job as a Python developer, I

highly encourage you to enroll in my Complete Python Course. Don’t waste your

time following disconnected, outdated tutorials. My Complete Python Course has

everything you need in one place:

• 12 hours of HD video
• Unlimited access - watch it as many times as you want
• Self-paced learning - take your time if you prefer
• Watch it online or download and watch offline
• Certificate of completion - add it to your resume to stand out
• 30-day money-back guarantee - no questions asked

The price for this course is $149 but the first 200 people who have downloaded this

cheat sheet can get it for $14.99 using the coupon code CHEATSHEET :

http://bit.ly/complete-python-course