Python-Cheat-Sheet.pdf

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1、Python   Cheat Sheet  Mosh Hamedani   Code with Mosh ()  1st Edition    About this Cheat Sheet  This cheat sheet includes the materials Ive covered in my Python tutorial for Beginners on YouTube. Both the YouTube tutorial and this cheat cover the core language cons

2、tructs 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    About the Author      Hi! My name is Mosh Hameda

3、ni. Im a software engineer with two decades of experience and Ive taught over three million how to code or how to become a professional software engineer. Its my mission to make software     engineering simple and accessible to everyone.               &nb

4、sp;                   Variables 5 . Comments 5 . Receiving Input 5 . Strings 6 . Arithmetic Operations 7 . If Statements 8 . Comparison operators 8 . While loops 8 . For loops 9 . Lists 9 . Tuples 9 . Dictionaries 10 . Functions 10 . Exceptions 11 . Class

5、es 11 . Inheritance 12 . Modules 12 . Packages 13 . Python Standard Library 13 . Pypi 14 . Want to Become a Python Expert? 14.   Variables  We use variables to temporarily store data in computers memory.  price = 10  rating = 4.9  course_name = Python for Beginners  is_

6、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. &

7、nbsp;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 youve written co

8、de in a certain way.  # This is a comment and it wont 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

9、a string. So, were converting the result into an integer by calling the built-in int() function.    Strings  We can define strings using single ( ) or double (“ “) quotes.  To define a multi-line string, we surround our string with tripe quotes (“”).  We can get individual c

10、haracters in a string using square brackets .  course = Python for Beginners  course0  # returns the first character  course1  # returns the second character  course-1 # returns the first character from the end   course-2 # returns the second character from the end

11、 We can slice a string using a similar notation:  course1:5  The above expression returns all the characters starting from the index position of 1 to 5 (but excluding 5). The result will be ytho  If we leave out the start index, 0 will be assumed.  If we leave out the end index,

12、the length of the string will be assumed.  We can use formatted strings to dynamically insert values into our strings:  name = Mosh  message = fHi, my name is name message.upper()  # to convert to uppercase message.lower()  # to convert to lowercase message.title()  # t

13、o capitalize the first letter of every word message.find(p) # returns the index of the first occurrence of p            (or -1 if not found)  message.replace(p, q)   To check if a string contains a character (or a sequence of characters), we use the in operato

14、r:  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 preceden

15、ce:  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

16、:  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

17、)  a != b (not equals)  While loops  i = 1  while i < 5:   print(i)   i += 1   For loops  for i in range(1, 5):    print(i)   range(5): generates 0, 1, 2, 3, 4   range(1, 5): generates 1, 2, 3, 4   range(1, 5, 2): generates 1, 3 &nb

18、sp;Lists  numbers = 1, 2, 3, 4, 5  numbers0  # returns the first item   numbers1      # returns the second item  numbers-1     # returns the first item from the end  numbers-2     # returns the second item from the end   numbers.a

19、ppend(6)  # adds 6 to the end  numbers.insert(0, 6) # adds 6 at index position of 0  numbers.remove(6)  # removes 6  numbers.pop()    # removes the last item  numbers.clear()   # removes all the items  numbers.index(8)   # returns the index of f

20、irst occurrence of 8  numbers.sort() # sorts the list  numbers.reverse()  # reverses the list  numbers.copy()    # returns a copy of the list  Tuples  They are like read-only lists. We use them to store a list of items. But once we define a tuple, we cannot ad

21、d or remove items or change the existing items.  coordinates = (1, 2, 3) We can unpack a list or a tuple into separate variables:  x, y, z = coordinates    Dictionaries  We use dictionaries to store key/value pairs.  customer =   “name”: “John Smith”,   “age”:

22、 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.g

23、et(“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, its easier to find bugs in a small chunk than the entire program. We c

24、an 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 posi

25、tion (order) matters   Keyword arguments: position doesnt 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 do

26、nt 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 ou

27、r programs. They often happen because of bad input or programming errors. Its 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 V

28、alueError:   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): &nb

29、sp;    print(“move”)        When a function is part of a class, we refer to it as a method.  Classes define templates or blueprints for creating objects. An object is an instance of a class. Every time we create a new instance, that instance follows the structure w

30、e define using the class.  point1 = Point(10, 5)  point2 = Point(2, 4) _init_ is a special method called constructor. It gets called at the time of creating new objects. We use it to initialize our objects.  Inheritance  Inheritance is a technique to remove code duplication. We c

31、an create a base class to define the common methods and then have other classes inherit these methods.  class Mammal:    def walk(self):     print(“walk”)    class Dog(Mammal):    def bark(self):     print(“bark”)  dog = Dog()  dog.wal

32、k()  # inherited from Mammal  dog.bark()  # defined in Dog   Modules  A module is a file with some Python code. We use modules to break up our program into multiple files. This way, our code will be better organized. We wont have one gigantic file with a million lines of cod

33、e in it!  There are 2 ways to import modules: we can import the entire module, or specific objects in a module.    # importing the entire converters module  import converters  converters.kg_to_lbs(5) # importing one function in the converters module  from converters imp

34、ort 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 ecommerc

35、e.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(

36、)    # 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

37、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 youre serious about learning Python and getting a job as a Python developer, I highly encourage you to

38、enroll in my Complete Python Course. Dont 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 y

39、ou 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