What is Python?
Python is a popular programming language. It was created by Guido van Rossum, and released in 1991.
To focus on the language itself this guide not includes any built-in modules like math, random, datetime, json, re, random, etc
Getting Started
Coding
Make a simple hello world
print('Hello, World!') # Hello, World!
Help
help(print)
# Prints the values to a stream, or to sys.stdout by default.
User Input
name = input("Enter your name:")
print("Your name is: " + name)
Run a python file
python helloworld.py
Comments
#This is a comment
print('Hello, World!')
Variables
name = 'John'
age = 42
x, y, z = 1, 2, 3
print('Name: ' + name) # Name: John
Data Types
# Text
string = 'Hello World'
# Numeric
integer = 20
float = 20.5
complex = 1j
# Sequence
list = ['apple', 'banana', 'cherry']
tuple = ('apple', 'banana', 'cherry') # Unchangeable
range = range(6)
# Mapping
dictionary = {'name' : 'John', 'age' : 36}
# Set - No duplicate members
set_value = {"apple", "banana", "cherry"}
frozenset_value = frozenset({"apple", "banana", "cherry"})
# Boolean
boolean = True
# Binary
bytes = b"Hello"
bytearray = bytearray(5)
memoryview = memoryview(bytes(5))
print(type(string)) # <class 'str'>
print(int('1')) # constructs an integer number
# Represents a null value
x = None
print(x) # None
Strings
hello = 'Hello, World! '
print(hello[0]) # H
print(hello[-1]) # !
print(hello[2:5]) # llo
print(len(hello)) # '13' get string length
print(hello.strip()) # 'Hello, World!' removes whitespaces
print(hello.lower()) # hello, world!
print(hello.upper()) # HELLO, WORLD!
print(hello.replace("H", "A")) # Aello, World!
print(hello.split(",")) # ['Hello', ' World!']
# Membership Operators
print("Hello" in hello) # True
print("Hello" not in hello) # False
print('Hello, ' + 'World!') # Hello, World!
print("{0}, World!".format('Hello')) # Hello, World!
Arithmetic
x, y = 1, 2
print(x + y) # Addition
print(x - y) # Subtraction
print(x * y) # Multiplication
print(x / y) # Division
print(x % y) # Modulus
print(x ** y) # Exponentiation
print(x // y) # Floor division
x += 3 # Same as x = x + 3
Comparison
x, y = 1, 2
print(x == y) # Equal
print(x != y) # Not equal
print(x > y) # Greater than
print(x < y) # Less than
print(x >= y) # Greater than or equal to
print(x <= y) # Less than or equal to
if b > a:
print("b is greater than a")
else:
print("b is not greater than a")
# Assert is used when debugging code
assert x == 2 # AssertionError is raised
Logical
x = 2
print(x == 2 and x > 42) # True
print(x == 2 or x > 42) # True
print(not(True)) # False
print(not(False)) # True
Identity
x = 'Hello'
z = x
y = 'World'
print(x is z) # True
print(x is y) # False
print(x == y) # False
Collections (Arrays)
list = ['hello', 'world']
print(list)
print(list[1])
print(list[-1])
print(list[2:5])
print(list[:4])
print(list[2:])
list[1] = "!"
print(thislist)
for x in thislist:
print(x)
if "apple" in thislist:
print("Yes, 'apple' is in the fruits list")
print(len(thislist))
list.append("orange") # Adds an element
list.clear() # Removes all the elements
mylist = list.copy() # Returns a copy of the list
list.count() # Number of elements
list.extend(['apple']) # Add the elements of a list
list.index() # Returns the index
list.insert(1, "orange") # Adds an element at
# the specified position
thislist.pop() # Removes the element
thislist.remove("banana") # Removes the first item
list.reverse() # Reverses the order
list.sort() # Sorts the list
del thislist[0]
mylist = thislist.copy()
list1 = ["a", "b" , "c"]
list2 = [1, 2, 3]
list3 = list1 + list2
thislist = list(("apple", "banana", "cherry"))
Sets
thisset = {"apple", "banana", "cherry"}
thisset.add("orange") # Add an item
thisset.update(["orange", "mango"]) # Add multiple items
print(len(thisset))
thisset.remove("banana")
set3 = set1.union(set2)
set1.update(set2)
Dictionaries
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
x = thisdict["model"]
print(thisdict)
thisdict["year"] = 2018
for x in thisdict.values():
print(x)
for x, y in thisdict.items():
print(x, y)
if "model" in thisdict:
print("Yes")
thisdict["color"] = "red" # Adding an item
thisdict.pop("model") # Removes the item
thisdict.popitem()
If ... Else
a = 200
b = 33
if b > a:
print("b is greater than a")
elif a == b:
print("a and b are equal")
else:
print("a is greater than b")
# Short Hand
if a > b: print("a is greater than b")
print("A") if a > b else print("B")
Loops
# While
while i < 6:
print(i)
i += 1
# break - can stop a loop
# continue - continue with the next
# For
fruits = ["apple", "banana", "cherry"]
for x in fruits:
print(x)
for x in range(6):
print(x)
# Function continues execution immediately
# after the last yield run
def number_generator():
yield 1
yield 2
for number in number_generator():
print(number)
# Output: 1 2
Functions
def my_function():
print("Hello from a function")
my_function()
def my_function(fname):
print(fname + " Refsnes")
my_function("Emil")
def my_function(*kids):
print("The youngest child is " + kids[2])
my_function("Emil", "Tobias", "Linus")
my_function(child1 = "Emil",
child2 = "Tobias",
child3 = "Linus")
# Default Parameter Value
def my_function(country = "Norway"):
print("I am from " + country)
my_function("Sweden")
my_function()
def my_function(x):
return 5 * x
print(my_function(3))
Lambda
# lambda arguments : expression
x = lambda a : a + 10
print(x(5))
Classes and Objects
class Person:
def __init__(self, name, age):
self.name = name
self.age = age
def myfunc(self):
print("Hello my name is " + self.name)
p1 = Person("John", 36)
p1.myfunc()
p1.age = 40 # Modify Object Properties
# Inheritance
class Student(Person):
pass # a statement that will do nothing
# Now the Student class has the same properties
# and methods as the Person class
x = Student("Mike", "Olsen")
x.printname()
Iterators
mytuple = ("apple", "banana", "cherry")
myit = iter(mytuple)
print(next(myit))
print(next(myit))
print(next(myit))
mytuple = ("apple", "banana", "cherry")
for x in mytuple:
print(x)
# Create an Iterator
class MyNumbers:
def __iter__(self):
self.a = 1
return self
def __next__(self):
x = self.a
self.a += 1
return x
myclass = MyNumbers()
myiter = iter(myclass)
print(next(myiter))
print(next(myiter))
print(next(myiter))
print(next(myiter))
print(next(myiter))
Scope
# Global variable
def myfunction():
global x = "hello"
myfunction()
print(x) # can be accessed outside the function
# Non Local Variable
def myfunc1():
x = "John"
def myfunc2():
nonlocal x
x = "hello"
myfunc2()
return x
print(myfunc1())
Modules
Save this code in a file named mymodule.py
def greeting(name):
print("Hello, " + name)
import mymodule
# import mymodule from greeting
# (import specific parts of a module)
mymodule.greeting("Jonathan")
# Create an alias for mymodule called mx
import mymodule as mx
a = mx.greeting("Jonathan")
Math
x = min(5, 10, 25)
y = max(5, 10, 25)
print(x)
print(y)
print(abs(-7.25))
print(pow(4, 3))
Try Except
try:
print(x)
except:
print("Something went wrong")
finally:
print("The 'try except' is finished")
x = -1
if x < 0:
raise Exception("Sorry, no numbers below zero")
File Handling
file = open("hello.txt", "r")
# r - Read
# a - Append
# w - Write
# x - Create
print(file.read())
print(file.readline())
file.close()
# Using with statement
with open('hello.txt', 'w') as file:
file.write('hello world !')
# no need to call file.close() when using with
All keywords
import keyword
keyword.kwlist
[ 'False', 'None', 'True', 'and', 'as', 'assert',
'break', 'class', 'continue', 'def', 'del', 'elif',
'else', 'except', 'finally', 'for', 'from', 'global',
'if', 'import', 'in', 'is', 'lambda', 'nonlocal',
'not', 'or', 'pass', 'raise', 'return', 'try', 'while',
'with','yield' ]
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