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Python Notes

This is my notes that I made while learning to code in
    Python

  • Python is a high-level, interpreted, interactive and object-oriented scripting language. Python is designed to be highly readable. It uses English keywords frequently where as other languages use punctuation, and it has fewer syntactical constructions than other languages.

  • Python can be used for:

    • Web Development (Server-Side)
    • Software Development
    • Mathematics
    • System Scripting

🔴 1. Variables

  • Variables are containers for storing data values.
  • Unlike other programming languages, Python has no command for declaring a variable. eg:
x = 5
y = "Hello, World!"
print(x)
print(y)

Output:

5
Hello, World!
  • Variable Names:
    • A variable name must start with a letter or the underscore character.
    • A variable name cannot start with a number.
    • A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ ).
    • Variable names are case-sensitive (age, Age and AGE are three different variables).
    • The variable name must not contain any special characters like !, @, #, $, % etc.
    • A variable name cannot be any of the Python keywords

🔴 2. Comments

  • Comments can be used to explain Python code.
  • Comments can be used to make the code more readable. eg:
# This is a comment
print("Hello, World!")

Output:

Hello, World!
  • Multi Line Comments
""" This is a comment
written in
more than just one line """
print("Hello, World!")

Output:

Hello, World!

🔴 3. Concatanation

  • To combine both text and a variable, Python uses the + character: eg:
x = "awesome"
print("Python is " + x)

Output:

Python is awesome
  • You can also use the + character to add a variable to another variable: eg:
x = "Python is "
y = "awesome"
z = x + y
print(z)

Output:

Python is awesome

🔴 Data Types

  • In programming, data type is an important concept.

  • Variables can store data of different types, and different types can do different things.

  • Python has the following data types built-in by default, in these categories:

    • Text Type: str
    • Numeric Types: int, float, complex
    • Sequence Types: list, tuple, range
    • Mapping Type: dict
    • Set Types: set, frozenset
    • Boolean Type: bool
    • Binary Types: bytes, bytearray, memoryview
    • None Type: NoneType

  • Setting data types:

x = "Hello World" # str
x = 20 # int
x = 20.5 # float
x = 1j # complex
x = ["apple", "banana", "cherry"] # list
x = ("apple", "banana", "cherry") # tuple
x = range(6) # range
x = {"name" : "John", "age" : 36} # dict
x = {"apple", "banana", "cherry"} # set
x = frozenset({"apple", "banana", "cherry"}) # frozenset
x = True # bool
x = b"Hello" # bytes
x = bytearray(5) # bytearray
x = memoryview(bytes(5)) # memoryview
x = None # NoneType
  • Setting the Specific Data Type:
x = str("Hello World") # str
x = int(20) # int
x = float(20.5) # float
x = complex(1j) # complex
x = list(("apple", "banana", "cherry")) # list
x = tuple(("apple", "banana", "cherry")) # tuple
x = range(6) # range
x = dict(name="John", age=36) # dict
x = set(("apple", "banana", "cherry")) # set
x = frozenset(("apple", "banana", "cherry")) # frozenset
x = bool(5) # bool
x = bytes(5) # bytes
x = bytearray(5) # bytearray
x = memoryview(bytes(5)) # memoryview

🔴 4. Numbers

  • There are three numeric types in Python:

    • int
      • Int, or integer, is a whole number, positive or negative, without decimals, of unlimited length.
    • float
      • Float, or "floating point number" is a number, positive or negative, containing one or more decimals.
    • complex
      • Complex numbers are written with a "j" as the imaginary part.

  • Variables of numeric types are created when you assign a value to them: eg:

    x = 1 # int
y = 2.8 # float
z = 1j # complex

  • Note: You cannot convert complext numbers into another number type.

  • Random Number:

import random
print(random.randrange(1, 10))

Output:

4

🔴 5. Casting

  • There may be times when you want to specify a type on to a variable. This can be done with casting.

  • Casting in python is therefore done using constructor functions:

    • int()
    • float()
    • str()

  • Integers:

    x = int(1) # x will be 1
y = int(2.8) # y will be 2
z = int("3") # z will be 3

  • Floats:

    x = float(1) # x will be 1.0
y = float(2.8) # y will be 2.8
z = float("3") # z will be 3.0
w = float("4.2") # w will be 4.2

  • Strings:

    x = str("s1") # x will be 's1'
y = str(2) # y will be '2'
z = str(3.0) # z will be '3.0'

🔴 6. Strings

  • Strings in python are surrounded by either single quotation marks, or double quotation marks.
  • str is the data type for strings in python.
  • You can display a string literal with the print() function:
print("Hello")
print('Hello')

Output:

Hello
Hello
  • Assigning a string to a variable:
a = "Hello"
print(a)

Output:

Hello
  • Multiline Strings:
a = """This is a multiline string,
come back, I still miss you,
but whocares,
hahaha"""
print(a)

Output:

This is a multiline string,
come back, I still miss you,
but whocares,
hahaha
  • Strings are Arrays:
a = "Hello, World!"
print(a[1])

Output:

e
  • Slicing:
b = "Hello, World!"
print(b[2:5])

Output:

llo
  • Negative Indexing:
b = "Hello, World!"
print(b[-5:-2])

Output:

orl
  • String Length:
a = "Hello, World!"
print(len(a))

Output:

13

  • String Methods:

    • strip() - Removes any whitespace from the beginning or the end
    • lower() - Returns the string in lower case
    • upper() - Returns the string in upper case
    • replace() - Replaces a string with another string
    • split() - Splits the string into substrings if it finds instances of the separator
    • capitalize() - Converts the first character to upper case
    • casefold() - Converts string into lower case
    • center() - Returns a centered string
    • count() - Returns the number of times a specified value occurs in a string
    • encode() - Returns an encoded version of the string
    • endswith() - Returns true if the string ends with the specified value
    • expandtabs() - Sets the tab size of the string
    • find() - Searches the string for a specified value and returns the position of where it was found
    • format() - Formats specified values in a string
    • index() - Searches the string for a specified value and returns the position of where it was found
    • isalnum() - Returns True if all characters in the string are alphanumeric
    • isalpha() - Returns True if all characters in the string are in the alphabet
    • isdecimal() - Returns True if all characters in the string are decimals
    • isdigit() - Returns True if all characters in the string are digits
    • isidentifier() - Returns True if the string is an identifier
    • islower() - Returns True if all characters in the string are lower case
    • isnumeric() - Returns True if all characters in the string are numeric
    • isprintable() - Returns True if all characters in the string are printable
    • isspace() - Returns True if all characters in the string are whitespaces
    • istitle() - Returns True if the string follows the rules of a title
    • isupper() - Returns True if all characters in the string are upper case
    • join() - Joins the elements of an iterable to the end of the string
    • ljust() - Returns a left justified version of the string
    • lstrip() - Returns a left trim version of the string
    • maketrans() - Returns a translation table to be used in translations
    • partition() - Returns a tuple where the string is parted into three parts
    • rfind() - Searches the string for a specified value and returns the last position of where it was found
    • rindex() - Searches the string for a specified value and returns the last position of where it was found
    • rjust() - Returns a right justified version of the string
    • rpartition() - Returns a tuple where the string is parted into three parts
    • rsplit() - Splits the string at the specified separator, and returns a list
    • rstrip() - Returns a right trim version of the string
    • splitlines() - Splits the string at line breaks and returns a list
    • startswith() - Returns true if the string starts with the specified value
    • swapcase() - Swaps cases, lower case becomes upper case and vice versa
    • title() - Converts the first character of each word to upper case
    • translate() - Returns a translated string
    • zfill() - Fills the string with a specified number of 0 values at the beginning

  • Check String:

    • isalnum() - Returns True if all characters in the string are alphanumeric
    • isalpha() - Returns True if all characters in the string are in the alphabet
    • isdecimal() - Returns True if all characters in the string are decimals
    • isdigit() - Returns True if all characters in the string are digits
    • isidentifier() - Returns True if the string is an identifier
    • islower() - Returns True if all characters in the string are lower case
    • isnumeric() - Returns True if all characters in the string are numeric
    • isprintable() - Returns True if all characters in the string are printable
    • isspace() - Returns True if all characters in the string are whitespaces
    • istitle() - Returns True if the string follows the rules of a title
    • isupper() - Returns True if all characters in the string are upper case

  • String Format:

    • format() - Formats specified values in a string
    • capitalize() - Converts the first character to upper case
    • casefold() - Converts string into lower case
    • center() - Returns a centered string
    • count() - Returns the number of times a specified value occurs in a string
    • encode() - Returns an encoded version of the string
    • endswith() - Returns true if the string ends with the specified value
    • expandtabs() - Sets the tab size of the string
    • find() - Searches the string for a specified value and returns the position of where it was found
    • index() - Searches the string for a specified value and returns the position of where it was found
    • join() - Joins the elements of an iterable to the end of the string
    • ljust() - Returns a left justified version of the string
    • lower() - Converts a string into lower case
    • lstrip() - Returns a left trim version of the string
    • maketrans() - Returns a translation table to be used in translations
    • partition() - Returns a tuple where the string is parted into three parts
    • replace() - Returns a string where a specified value is replaced with a specified value
    • rfind() - Searches the string for a specified value and returns the last position of where it was found
    • rindex() - Searches the string for a specified value and returns the last position of where it was found
    • rjust() - Returns a right justified version of the string
    • rpartition() - Returns a tuple where the string is parted into three parts
    • rsplit() - Splits the string at the specified separator, and returns a list
    • rstrip() - Returns a right trim version of the string
    • split() - Splits the string at the specified separator, and returns a list
    • splitlines() - Splits the string at line breaks and returns a list
    • startswith() - Returns true if the string starts with the specified value
    • strip() - Returns a trimmed version of the string
    • swapcase() - Swaps cases, lower case becomes upper case and vice versa
    • title() - Converts the first character of each word to upper case

  • Check if a certain phrase or character is present in a string

    txt = "God is watching."
x = "NOT" in txt
print(x)

    Output:

    False

  • Check if a certain phrase or character is NOT present in a string

    txt = "Saturn is my favourite planet."
x = "Earth" not in txt
print(x)

    Output:

    True

  • String Concatenation:

    a = "Hello"
b = "World"
c = a + b
print(c)

    Output:

    HelloWorld

  • String Format:

    age = 36
txt = "My name is John, and I am {}"
print(txt.format(age))

    Output:

    My name is John, and I am 36

  • Escape Character:

    • To insert characters that are illegal in a string, use an escape character.
    • An escape character is a backslash \ followed by the character you want to insert.
    • An example of an illegal character is a double quote inside a string that is surrounded by double quotes:
    txt = "We are the so-called \"Vikings\" from the north."
print(txt)

    Output:

    We are the so-called "Vikings" from the north.

🔴 7. Booleans

  • Booleans represent one of two values: True or False.
  • In programming you often need to know if an expression is True or False.

🔴 8. Python Operators

  • Operators are used to perform operations on variables and values.

  • Python divides the operators in the following groups:

    • Arithmetic operators
    • Assignment operators
    • Comparison operators
    • Logical operators
    • Identity operators
    • Membership operators
    • Bitwise operators

  • Arithmetic Operators:

    • + - Addition
    • - - Subtraction
    • * - Multiplication
    • / - Division
    • % - Modulus
    • ** - Exponentiation
    • // - Floor division

  • Assignment Operators:

    • = - x = 5
    • += - x += 3
    • -= - x -= 3
    • *= - x *= 3
    • /= - x /= 3
    • %= - x %= 3
    • //= - x //= 3
    • **= - x **= 3
    • &= - x &= 3
    • |= - x |= 3
    • ^= - x ^= 3
    • >>= - x >>= 3
    • <<= - x <<= 3

  • Comparison Operators:

    • == - Equal
    • != - Not equal
    • > - Greater than
    • < - Less than
    • >= - Greater than or equal to
    • <= - Less than or equal to

  • Logical Operators:

    • and - Returns True if both statements are true
    • or - Returns True if one of the statements is true
    • not - Reverse the result, returns False if the result is true

  • Identity Operators:

    • is - Returns True if both variables are the same object
    • is not - Returns True if both variables are not the same object

  • Membership Operators:

    • in - Returns True if a sequence with the specified value is present in the object
    • not in - Returns True if a sequence with the specified value is not present in the object

  • Bitwise Operators:

    • & - AND
    • | - OR
    • ^ - XOR
    • ~ - NOT
    • << - Zero fill left shift
    • >> - Signed right shift

🔴 9. Lists

  • Lists are used to store multiple items in a single variable.
  • Lists are created using square brackets:
thislist = ["apple", "banana", "cherry"]
print(thislist)

Output:

['apple', 'banana', 'cherry']

  • List Items:

    • List items are ordered, changeable, and allow duplicate values.
    • List items are indexed, the first item has index [0], the second item has index [1] etc.

  • List Items - Data Types:

    • List items can be of any data type:
    list1 = ["apple", "banana", "cherry"]
list2 = [1, 5, 7, 9, 3]
list3 = [True, False, False]

  • A list can contain different data types:

    list1 = ["apple", "banana", "cherry"]
list2 = [1, 5, 7, 9, 3]
list3 = [True, False, False]
list4 = ["apple", 5, True, "banana", "cherry"]

  • type():

    • From Python's perspective, lists are defined as objects with the data type 'list':
    mylist = ["apple", "banana", "cherry"]
print(type(mylist))

    Output:

    <class 'list'>

🔴 10. Tuples

  • Tuples are used to store multiple items in a single variable.
  • A tuple is a collection which is ordered and unchangeable.
  • Tuples are written with round brackets.
thistuple = ("apple", "banana", "cherry")
print(thistuple)

Output:

('apple', 'banana', 'cherry')

  • Tuple Items:

    • Tuple items are ordered, unchangeable, and allow duplicate values.
    • Tuple items are indexed, the first item has index [0], the second item has index [1] etc.

  • Tuple Items - Data Types:

    • Tuple items can be of any data type:
    tuple1 = ("apple", "banana", "cherry")
tuple2 = (1, 5, 7, 9, 3)
tuple3 = (True, False, False)

  • A tuple can contain different data types:

    tuple1 = ("apple", "banana", "cherry")
tuple2 = (1, 5, 7, 9, 3)
tuple3 = (True, False, False)
tuple4 = ("apple", 5, True, "banana", "cherry")

  • type(): - From Python's perspective, tuples are defined as objects with the data type 'tuple':

      mytuple = ("apple", "banana", "cherry")
  print(type(mytuple))

    Output:

      <class 'tuple'>

🔴 11. Sets

  • Sets are used to store multiple items in a single variable.
  • A set is a collection which is both unordered and unindexed.
  • Sets are written with curly brackets.
thisset = {"apple", "banana", "cherry"}
print(thisset)

Output:

{'apple', 'banana', 'cherry'}

  • Set Items:

    • Set items are unordered, unchangeable, and do not allow duplicate values.
    • Set items are indexed, the first item has index [0], the second item has index [1] etc.

  • Set Items - Data Types:

    • Set items can be of any data type:
    set1 = {"apple", "banana", "cherry"}
set2 = {1, 5, 7, 9, 3}
set3 = {True, False, False}

  • A set can contain different data types:

    set1 = {"apple", "banana", "cherry"}
set2 = {1, 5, 7, 9, 3}
set3 = {True, False, False}
set4 = {"apple", 5, True, "banana", "cherry"}

  • type(): - From Python's perspective, sets are defined as objects with the data type 'set':

      myset = {"apple", "banana", "cherry"}
  print(type(myset))

    Output:

      <class 'set'>

🔴 12. Dictionaries

  • Dictionaries are used to store data values in key:value pairs.
  • A dictionary is a collection which is ordered*, changeable and does not allow duplicates.
  • Dictionaries are written with curly brackets, and have keys and values.
thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
print(thisdict)

Output:

{'brand': 'Ford', 'model': 'Mustang', 'year': 1964}

  • Dictionary Items:

    • Dictionary items are ordered, changeable, and does not allow duplicates.
    • Dictionary items are indexed, the first item has index [0], the second item has index [1] etc.

  • Dictionary Items - Data Types:

    • Dictionary items can be of any data type:
    thisdict = {
  "brand": "Ford",
  "electric": False,
  "year": 1964,
  "colors": ["red", "white", "blue"]
}

  • type(): - From Python's perspective, dictionaries are defined as objects with the data type 'dict':

      mydict = {
    "brand": "Ford",
    "model": "Mustang",
    "year": 1964
  }
  print(type(mydict))

    Output:

      <class 'dict'>

🔴 13. If...Else

  • Python supports the usual logical conditions from mathematics:

    • Equals: a == b
    • Not Equals: a != b
    • Less than: a < b
    • Less than or equal to: a <= b
    • Greater than: a > b
    • Greater than or equal to: a >= b
a = 33
b = 200
if b > a:
  print("b is greater than a")

Output:

b is greater than a

  • Elif:

    • The elif keyword is pythons way of saying "if the previous conditions were not true, then try this condition".
a = 33
b = 33
if b > a:
  print("b is greater than a")
elif a == b:
  print("a and b are equal")

Output:

a and b are equal

  • Else:

    • The else keyword catches anything which isn't caught by the preceding conditions.
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")

Output:

a is greater than b

  • Short Hand If:

    • If you have only one statement to execute, you can put it on the same line as the if statement.
if a > b: print("a is greater than b")

Output:

a is greater than b

  • Short Hand If...Else:

    • If you have only one statement to execute, one for if, and one for else, you can put it all on the same line.
a = 2
b = 330
print("A") if a > b else print("B")

Output:

B

  • And:

    • The and keyword is a logical operator, and is used to combine conditional statements.
a = 200
b = 33
c = 500
if a > b and c > a:
  print("Both conditions are True")

Output:

Both conditions are True

  • Or:

    • The or keyword is a logical operator, and is used to combine conditional statements.
a = 200
b = 33
c = 500
if a > b or a > c:
  print("At least one of the conditions is True")

Output:

At least one of the conditions is True

  • Nested If:

    • You can have if statements inside if statements, this is called nested if statements.
x = 41
if x > 10:
  print("Above ten,")
  if x > 20:
    print("and also above 20!")
  else:
    print("but not above 20.")

Output:

Above ten,
and also above 20!

🔴 14. While Loops

  • With the while loop we can execute a set of statements as long as a condition is true.
i = 1
while i < 6:
  print(i)
  i += 1

Output:

1
2
3
4
5

  • The break Statement:

    • With the break statement we can stop the loop even if the while condition is true.
i = 1
while i < 6:
  print(i)
  if i == 3:
    break
  i += 1

Output:

1
2
3

  • The continue Statement:

    • With the continue statement we can stop the current iteration, and continue with the next.
i = 0
while i < 6:
  i += 1
  if i == 3:
    continue
  print(i)

Output:

1
2
4
5
6

  • The else Statement:

    • With the else statement we can run a block of code once when the condition no longer is true.
i = 1
while i < 6:
  print(i)
  i += 1
else:
  print("i is no longer less than 6")

Output:

1
2
3
4
5
i is no longer less than 6

🔴 15. For Loops

  • A for loop is used for iterating over a sequence (that is either a list, a tuple, a dictionary, a set, or a string).
fruits = ["apple", "banana", "cherry"]
for x in fruits:
  print(x)

Output:

apple
banana
cherry
  • Looping Through a String:
for x in "banana":
  print(x)

Output:

b
a
n
a
n
a

  • The break Statement:

    • With the break statement we can stop the loop before it has looped through all the items.
fruits = ["apple", "banana", "cherry"]
for x in fruits:
  print(x)
  if x == "banana":
    break

Output:

apple
banana

  • The continue Statement:

    • With the continue statement we can stop the current iteration of the loop, and continue with the next.
fruits = ["apple", "banana", "cherry"]
for x in fruits:
  if x == "banana":
    continue
  print(x)

Output:

apple
cherry

  • The range() Function:

    • To loop through a set of code a specified number of times, we can use the range() function.
for x in range(6):
  print(x)

Output:

0
1
2
3
4
5

  • The range() Function:

    • The range() function defaults to 0 as a starting value, however it is possible to specify the starting value by adding a parameter: range(2, 6), which means values from 2 to 6 (but not including 6):
for x in range(2, 6):
  print(x)

Output:

2
3
4
5

  • The range() Function:

    • The range() function defaults to increment the sequence by 1, however it is possible to specify the increment value by adding a third parameter: range(2, 30, 3):
for x in range(2, 30, 3):
  print(x)

Output:

2
5
8
11
14
17
20
23
26
29

  • Else in For Loop:

    • The else keyword in a for loop specifies a block of code to be executed when the loop is finished.
for x in range(6):
  print(x)
else:
  print("Finally finished!")

Output:

0
1
2
3
4
5
Finally finished!

  • Nested Loops:

    • A nested loop is a loop inside a loop.
    • The "inner loop" will be executed one time for each iteration of the "outer loop".
adj = ["red", "big", "tasty"]
fruits = ["apple", "banana", "cherry"]

for x in adj:
  for y in fruits:
    print(x, y)

Output:

red apple
red banana
red cherry
big apple
big banana
big cherry
tasty apple
tasty banana
tasty cherry

🔴 16. Functions

  • A function is a block of code which only runs when it is called.
  • You can pass data, known as parameters, into a function.
  • A function can return data as a result.
def my_function():
  print("Hello from a function")

my_function()

Output:

Hello from a function

  • Arguments:

    • Information can be passed into functions as arguments.
def my_function(fname):
  print(fname + " Kumar")

my_function("Rahul")
my_function("Rohit")
my_function("Raj")

Output:

Rahul Kumar
Rohit Kumar
Raj Kumar

  • Number of Arguments:

    • By default, a function must be called with the correct number of arguments. Meaning that if your function expects 2 arguments, you have to call the function with 2 arguments, not more, and not less.
def my_function(fname, lname):
  print(fname + " " + lname)

my_function("Rahul", "Kumar")

Output:

Rahul Kumar

  • Arbitrary Arguments, *args:

    • If you do not know how many arguments that will be passed into your function, add a * before the parameter name in the function definition.
def my_function(*kids):
  print("The youngest child is " + kids[2])

my_function("Emil", "Tobias", "Linus")

Output:

The youngest child is Linus

  • Keyword Arguments:

    • You can also send arguments with the key = value syntax.
def my_function(child3, child2, child1):
  print("The youngest child is " + child3)

my_function(child1 = "Emil", child2 = "Tobias", child3 = "Linus")

Output:

The youngest child is Linus

  • Arbitrary Keyword Arguments, **kwargs:

    • If you do not know how many keyword arguments that will be passed into your function, add two asterisk: ** before the parameter name in the function definition.
def my_function(**kid):
  print("His last name is " + kid["lname"])

my_function(fname = "Aditya", lname = "Raj")

Output:

His last name is Raj

  • Default Parameter Value:

    • The following example shows how to use a default parameter value.
def my_function(country = "India"):
  print("I am from " + country)

my_function("Sweden")
my_function("Norway")
my_function()
my_function("Brazil")

Output:

I am from Sweden
I am from Norway
I am from India
I am from Brazil

  • Passing a List as an Argument:

    • You can send any data types of argument to a function (string, number, list, dictionary etc.), and it will be treated as the same data type inside the function.
def my_function(food):
  for x in food:
    print(x)

fruits = ["apple", "banana", "cherry"]
my_function(fruits)

Output:

apple
banana
cherry

  • Return Values:

    • To let a function return a value, use the return statement.
def my_function(x):
  return 5 * x

print(my_function(3))
print(my_function(5))
print(my_function(9))

Output:

15
25
45

  • The pass Statement:

    • function definitions cannot be empty, but if you for some reason have a function definition with no content, put in the pass statement to avoid getting an error.
def myfunction():
  pass

🔴 17. Lambda

  • A lambda function is a small anonymous function.
  • A lambda function can take any number of arguments, but can only have one expression.
x = lambda a : a + 10
print(x(5))

Output:

15
  • Lambda functions can take any number of arguments:
x = lambda a, b : a * b
print(x(5, 6))

Output:

30
x = lambda a, b, c : a + b + c
print(x(5, 6, 2))

Output:

13

  • Why Use Lambda Functions?

    • The power of lambda is better shown when you use them as an anonymous function inside another function.
def myfunc(n):
  return lambda a : a * n

mydoubler = myfunc(2)
mytripler = myfunc(3)

print(mydoubler(11))
print(mytripler(11))

Output:

22
33

🔴 18. Arrays

  • Arrays are used to store multiple values in one single variable.
cars = ["Ford", "Volvo", "BMW"]

  • Access the Elements of an Array:

    • You refer to an array element by referring to the index number.
x = cars[0]
  • Modify the value of the first array item:
cars[0] = "Toyota"

  • The Length of an Array:

    • Use the len() method to return the length of an array (the number of elements in an array).
x = len(cars)

  • Looping Array Elements:

    • You can use the for in loop to loop through all the elements of an array.
for x in cars:
  print(x)

  • Adding Array Elements:

    • You can use the append() method to add an element to an array.
cars.append("Honda")

  • Removing Array Elements:

    • You can use the pop() method to remove an element from the array.
cars.pop(1)

  • Array Methods:

    • append() - Adds an element at the end of the list
    • clear() - Removes all the elements from the list
    • copy() - Returns a copy of the list
    • count() - Returns the number of elements with the specified value
    • extend() - Add the elements of a list (or any iterable), to the end of the current list
    • index() - Returns the index of the first element with the specified value
    • insert() - Adds an element at the specified position
    • pop() - Removes the element at the specified position
    • remove() - Removes the first item with the specified value
    • reverse() - Reverses the order of the list
    • sort() - Sorts the list

🔴 19. Classes/Objects

  • Python is an object oriented programming language.

  • Almost everything in Python is an object, with its properties and methods.

  • A Class is like an object constructor, or a "blueprint" for creating objects.

class MyClass:
  x = 5

  • Create an Object:

    • Now we can use the class named MyClass to create objects.
p1 = MyClass()
print(p1.x)

Output:

5

  • The __init__() Function:

    • The examples above are classes and objects in their simplest form, and are not really useful in real life applications.
    • To understand the meaning of classes we have to understand the built-in __init__() function.
    • All classes have a function called __init__(), which is always executed when the class is being initiated.
    • Use the __init__() function to assign values to object properties, or other operations that are necessary to do when the object is being created.
class Person:
  def __init__(self, name, age):
    self.name = name
    self.age = age

p1 = Person("John", 36)

print(p1.name)
print(p1.age)

Output:

John
36

  • Object Methods:

    • Objects can also contain methods. Methods in objects are functions that belong to the object.
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()

Output:

Hello my name is John

  • The self Parameter:

    • The self parameter is a reference to the current instance of the class, and is used to access variables that belong to the class.
class Person:
  def __init__(mysillyobject, name, age):
    mysillyobject.name = name
    mysillyobject.age = age

  def myfunc(abc):
    print("Hello my name is " + abc.name)

p1 = Person("John", 36)
p1.myfunc()

Output:

Hello my name is John

  • Modify Object Properties:

    • You can modify properties on objects like this:
p1.age = 40

  • Delete Object Properties:

    • You can delete properties on objects by using the del keyword:
del p1.age

  • Delete Objects:

    • You can delete objects by using the del keyword:
del p1

🔴 20. Inheritance

  • Inheritance allows us to define a class that inherits all the methods and properties from another class.

  • Parent Class:

    • The class being inherited from is called the parent class.
class Person:
  def __init__(self, fname, lname):
    self.firstname = fname
    self.lastname = lname

  def printname(self):
    print(self.firstname, self.lastname)

x = Person("John", "Doe")
x.printname()

Output:

John Doe

  • Child Class:

    • The class that inherits from another class is called the child class.
class Student(Person):
  pass

  • Use the super() Function:

    • The super() function is used to give access to methods and properties of a parent or sibling class.
class Student(Person):
  def __init__(self, fname, lname):
    super().__init__(fname, lname)

x = Student("Aditya", "Raj")
x.printname()

Output:

Aditya Raj

  • Add Properties:

    • Add a property called graduationyear to the Student class.
class Student(Person):
  def __init__(self, fname, lname, year):
    super().__init__(fname, lname)
    self.graduationyear = year

x = Student("Aditya", "Raj", 2027)

  • Add Methods:

    • Add a method called welcome to the Student class.
class Student(Person):
  def __init__(self, fname, lname, year):
    super().__init__(fname, lname)
    self.graduationyear = year

  def welcome(self):
    print("Welcome", self.firstname, self.lastname, "to the class of", self.graduationyear)

x = Student

🔴 21. User Input

  • Python allows for user input.
username = input("Enter username:")
print("Username is: " + username)

Output:

Enter username: Aditya
Username is: Aditya

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Notes that I made while learning Python

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