pythonidae

A simple python practicing space

DATATYPES

Basic Python Datatypes

int

The basic datatype used in performing basic operation, =>

# Arithmetic
  2 + 4 # the '+' used to perfom operation
  2 - 1
  10 + 3  # 13
  10 - 3  # 7
  10 * 3  # 30
  10 ** 3 # 1000

float

This is a number type also but with the decimal number

  # Arithmetic
  20.34 + 2
  10 + 3  # 13
  10 - 3  # 7
  10 * 3  # 30
  10 ** 3 # 1000
  10 / 3  # 3.3333333333333335
  10 // 3 # 3 --> floor division - no decimals and returns an int
  10 % 3  # 1 --

bool

This is a truthy datatype that has either 'True' or 'False'

 True
 False

str

The str is a a strings datatype, mostly used with the double or single quote ("", ''),

  name = "samuel"

  '''
  This is a multi-line
  string type
  ''' #multi-line string

  f'Hello {name} this is a formated string, i hope you know that '


  len('turtle') # 6

  # Basic Methods
  '  I am alone '.strip()               # 'I am alone' --> Strips all whitespace characters from both ends.
  'On an island'.strip('d')             # 'On an islan' --> # Strips all passed characters from both ends.
  'but life is good!'.split()           # ['but', 'life', 'is', 'good!']
  'Help me'.replace('me', 'you')        # 'Help you' --> Replaces first with second param
  'Need to make fire'.startswith('Need')# True
  'and cook rice'.endswith('rice')      # True
  'still there?'.upper()                # STILL THERE?
  'HELLO?!'.lower()                     # hello?!
  'ok, I am done.'.capitalize()         # 'Ok, I am done.'
  'oh hi there'.count('e')              # 2
  'bye bye'.index('e')                  # 2
  'oh hi there'.find('i')               # 4 --> returns the starting index position of the first occurrence
  'oh hi there'.find('a')               # -1
  'oh hi there'.index('a')              # Raises ValueError

  'I\'m thirsty'
  "I'm thirsty"
  "\n" # new line
  "\t" # adds a tab

  'Hey you!'[4] # y
  name = 'Coded Hola'
  name[4]     # d
  name[:]     # Coded Hola
  name[:1]    # C
  name[-1]    # a
  name[::1]   # Coded Hola
  name[::-1]  # aloh dedoc
  # : is called slicing and has the format [ start : end : step ]

  'Hi there ' + 'Timmy' # 'Hi there Timmy' --> This is called string concatenation
  '*'*10 # **********

list

This datatype is used to hold a list of datatypes in sequence, and this starts count from 0

  software_stacks = ["javascript", "python", "c++"]

tuple

Tuple Like lists, but they are used for immutable thing (that don't change) To declare a tuple we => my_tuple = ('apple','grapes','mango', 'grapes')

set

Set is an unordered collection of unique objects. sets are created like object but only values are required => my_set = { 1, 2, 3, 4, 5 }

Note => They are no duplicates in set

dict

This is a tyoe of datatype that stores values in "key":"value" pairs

  user_details = {
    "name": "coded hola",
    "stacks": ["python", "typescript"],
    "isDev": True
  }

Classes --> Custom types

These are data types that we create

Specialized data types

These are special package or modules that we can bring to python

None

This datatype means nothing in python i.e absence of value

BUILT-IN FUNCTIONS

Basic python function

They are ome basic python function utility that needs to be known

type

  type(4)                  # int
  type(2.10)               # float
  type('Coded hola')       # str
  type(True)               # bool
  type([1, 3, "sam"])      # list
  type({"name": "john"})   # dict

print

 print("Hello") # prints hello to the console

VARIABLES

This is a way of storing information, we declare a variable and assign a datatype to it to hold the datatype for use in a later time (binding) some important things to consider in naming a variable are

• start with lowercase or _ (underscore)
• can be snake case i.e (_)underscore in the middle)
• They are case sensitive
• Don't override python or module keywords
• store constants in UPPERCASE
• Don't create a variable with double __(underscore). They are reserved words for that

user_name = 'coded hola'
developer = True
NAME = 'samuel'

'list' methods

  # Add to List
  my_list * 2                # [1, 2, '3', True, 1, 2, '3', True]
  my_list + [100]            # [1, 2, '3', True, 100] --> doesn't mutate original list, creates new one
  my_list.append(100)        # None --> Mutates original list to [1, 2, '3', True, 100]          # Or: <list> += [<el>]
  my_list.extend([100, 200]) # None --> Mutates original list to [1, 2, '3', True, 100, 200]
  my_list.insert(2, '!!!')   # None -->  [1, 2, '!!!', '3', True] - Inserts item at index and moves the rest to the right.

  ' '.join(['Hello','There'])# 'Hello There' --> Joins elements using string as separator.

  # Copy a List
  basket = ['apples', 'pears', 'oranges']
  new_basket = basket.copy()
  new_basket2 = basket[:]

  # Remove from List
  [1,2,3].pop()    # 3 --> mutates original list, default index in the pop method is -1 (the last item)
  [1,2,3].pop(1)   # 2 --> mutates original list
  [1,2,3].remove(2)# None --> [1,3] Removes first occurrence of item or raises ValueError.
  [1,2,3].clear()  # None --> mutates original list and removes all items: []
  del [1,2,3][0]   # None --> removes item on index 0 or raises IndexError

  [1,2,'b',4,5,6].index('b') # return ==> b which is the index
  ['a','b','c','d','e'].index('b', 0, 4) # return ==> b because b is present in the index between 0 to 4
  [1,2,'b',4,5,6].index('a') # return ==> An Error => Advisable to use a different method is not sure index is present

  # The 'in' method is considered safe in this context because it returns 'True' or 'false'
  'x' in ['a', 'b', 'c', 'd'] # returns False



  [1,2,5,3].sort()         # None --> Mutates list to [1, 2, 3, 5]
  [1,2,5,3].sort(reverse=True) # None --> Mutates list to [5, 3, 2, 1]
  [1,2,5,3].reverse()      # None --> Mutates list to [3, 5, 2, 1]
  sorted([1,2,5,3])        # [1, 2, 3, 5] --> new list created
  my_list = [(4,1),(2,4),(2,5),(1,6),(8,9)]
  sorted(my_list,key=lambda x: int(x[0])) # [(1, 6), (2, 4), (2, 5), (4, 1), (8, 9)] --> sort the list by 1st (0th index) value of the tuple
  list(reversed([1,2,5,3]))# [3, 5, 2, 1] --> reversed() returns an iterator

  my_list[::-1] # This reverse a list and also make a new copy(doesn't modify the old list)

  stacks = ['python', 'javscript', 'c++', 'go']
  " ".join(stacks)

'dict' methods

  my_dict = {'name': 'Andrei Neagoie', 'age': 30, 'magic_power': False}
  my_dict['name']                      # Andrei Neagoie
  len(my_dict)                         # 3
  list(my_dict.keys())                 # ['name', 'age', 'magic_power']
  list(my_dict.values())               # ['Andrei Neagoie', 30, False]
  list(my_dict.items())                # [('name', 'Andrei Neagoie'), ('age', 30), ('magic_power', False)]
  my_dict['favourite_snack'] = 'Grapes'# {'name': 'Andrei Neagoie', 'age': 30, 'magic_power': False, 'favourite_snack': 'Grapes'}
  my_dict.get('age')                   # 30 --> Returns None if key does not exist.
  my_dict.get('ages', 0 )              # 0 --> Returns default (2nd param) if key is not found

  #Remove key
  del my_dict['name']
  my_dict.pop('name', None)

  my_dict.update({'cool': True})  # {'name': 'Andrei Neagoie', 'age': 30, 'magic_power': False, 'favourite_snack': 'Grapes', 'cool': True}
  {**my_dict, **{'cool': True} }                                         # {'name': 'Andrei Neagoie', 'age': 30, 'magic_power': False, 'favourite_snack': 'Grapes', 'cool': True}
  new_dict = dict([['name','Andrei'],['age',32],['magic_power',False]])  # Creates a dict from collection of key-value pairs.
  new_dict = dict(zip(['name','age','magic_power'],['Andrei',32, False]))# Creates a dict from two collections.
  new_dict = my_dict.pop('favourite_snack')  # Removes item from dictionary.

  # Dictionary Comprehension
  {key: value for key, value in new_dict.items() if key == 'age' or key == 'name'} # {'name': 'Andrei', 'age': 32} --> Filter dict by keys

'tuples' methods

  len(my_tuple)                          # 4
  my_tuple[2]                            # mango
  my_tuple[-1]                           # 'grapes'

  # Immutability
  my_tuple[1] = 'donuts'  # TypeError
  my_tuple.append('candy')# AttributeError

  # Methods
  my_tuple.index('grapes') # 1
  my_tuple.count('grapes') # 2

'sets' methods

  new_set = {1, 2, 3, 4, 5, 6}

  my_set.remove(100)      # {1} --> Raises KeyError if element not found
  my_set.discard(100)     # {1} --> Doesn't raise an error if element not found
  my_set.clear()          # {}
  new_set = {1,2,3}.copy()# {1,2,3}

  # set method
  set1 = {1,2,3}
  set2 = {3,4,5}
  set3 = set1.union(set2)               # {1,2,3,4,5}
  set4 = set1.intersection(set2)        # {3}
  set5 = set1.difference(set2)          # {1, 2}
  set6 = set1.symmetric_difference(set2)# {1, 2, 4, 5}
  set1.issubset(set2)                   # False
  set1.issuperset(set2)                 # False
  set1.isdisjoint(set2)                 # False --> return True if two sets have a null intersection.

Conditionals

Comparison Operators and Logical Operators

==                   # equal values
!=                   # not equal
>                    # left operand is greater than right operand
<                    # left operand is less than right operand
>=                   # left operand is greater than or equal to right operand
<=                   # left operand is less than or equal to right operand
<element> is <element> # check if two operands refer to same object in memory
Logical Operators
1 < 2 and 4 > 1 # True
1 > 3 or 4 > 1  # True
1 is not 4      # True
not True        # False
1 not in [2,3,4]# True


if <condition that evaluates to boolean>:
  # perform action1
elif <condition that evaluates to boolean>:
  # perform action2
else:
  # perform action3

## TERNARY OPERATOR IN PYTHON
is_friend = True
can_message = "Message Allowed" if is_friend else "not allowed"

Control flow

  my_list = [1,2,3]
  my_tuple = (1,2,3)
  my_list2 = [(1,2), (3,4), (5,6)]
  my_dict = {'a': 1, 'b': 2. 'c': 3}

  for num in my_list:
      print(num) # 1, 2, 3

  for num in my_tuple:
      print(num) # 1, 2, 3

  for num in my_list2:
      print(num) # (1,2), (3,4), (5,6)

  for num in '123':
      print(num) # 1, 2, 3

  for idx,value in enumerate(my_list):
      print(idx) # get the index of the item
      print(value) # get the value

  for k,v in my_dict.items(): # Dictionary Unpacking
      print(k) # 'a', 'b', 'c'
      print(v) # 1, 2, 3

  while <condition that evaluates to boolean>:
    # action
    if <condition that evaluates to boolean>:
      break # break out of while loop
    if <condition that evaluates to boolean>:
      continue # continue to the next line in the block

    # WHILE LOOPS IS GREAT WHEN YOU DON'T KNOW WHEN THE TASK IS END
    # EXAMPLE
    # waiting until user quits
  msg = ''
  while msg != 'quit':
      msg = input("What should I do?")
      print(msg)

Range

  for _ in range(0, 5):
    print(_)

  for _ in range(0, 10, 2):
    print(_)

  for _ in range(10, 1, -1):
    print(_)

Enumerate

This method returns both the index and the value counter of the item that is being looped through

  for i, el in enumerate('helloo'):
  print(f'{i}, {el}')
  # 0, h
  # 1, e
  # 2, l
  # 3, l
  # 4, o
  # 5, o

Functions

A function in python is defined using the 'def' key word then naming the function.

  def add(msg):
    return msg

  print(add("Hello functions")) # Hello functions