Python

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• Python is an interpreted, high-level and general-purpose, dynamically typed programming language

• It is also Object oriented, modular oriented and a scripting language.

• In Python, everything is considered as an Object.

• A python file has an extension of .py

• Python follows Indentation to separate code blocks instead of flower brackets({}).

• We can run a python file by the following command in cmd(Windows) or shell(mac/linux).

  $ python <filename.py> or $ python3 <filename.py>

By default, python doesn’t require any imports to run a python file.

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Create and execute a program

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1. Open up a terminal/cmd
2. Create the program: nano/cat > nameProgram.py
3. Write the program and save it
4. python nameProgram.py

Basic Datatypes

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Keywords

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• As of python3.8 there are 35 keywords

Operators

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Basic Data Structures

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List

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• List is a collection which is ordered and changeable. Allows duplicate members.
• Lists are created using square brackets:

thislist = ["apple", "banana", "cherry"] 

• 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.
• The list is changeable, meaning that we can change, add, and remove items in a list after it has been created.
• To determine how many items a list has, use the len() function.
• A list can contain different data types:

list1 = ["abc", 34, True, 40, "male"]

• It is also possible to use the list() constructor when creating a new list

thislist = list(("apple", "banana", "cherry"))  # note the double round-brackets

• pop() function removes the last value in the given list by default.

  thislist = ["apple", "banana", "cherry"] 
  
  print(thislist.pop())  # cherry
  print(thislist.pop(0))  #apple 
  

Tuple

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• Tuple is a collection which is ordered and unchangeable. Allows duplicate members.
• A tuple is a collection which is ordered and unchangeable.
• Tuples are written with round brackets.

thistuple = ("apple", "banana", "cherry")

• 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.
• When we say that tuples are ordered, it means that the items have a defined order, and that order will not change.
• Tuples are unchangeable, meaning that we cannot change, add or remove items after the tuple has been created.
• Since tuple are indexed, tuples can have items with the same value:
• Tuples allow duplicate values:

thistuple = ("apple", "banana", "cherry", "apple", "cherry")

• To determine how many items a tuple has, use the len()function:

thistuple = ("apple", "banana", "cherry")
print(len(thistuple))

• To create a tuple with only one item, you have to add a comma after the item, otherwise Python will not recognize it as a tuple.

thistuple = ("apple",)
print(type(thistuple))

# NOT a tuple
thistuple = ("apple")
print(type(thistuple))

• It is also possible to use the tuple() constructor to make a tuple.

thistuple = tuple(("apple", "banana", "cherry")) # note the double round-brackets
print(thistuple)

Set

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• Set is a collection which is unordered and unindexed. No duplicate members.
• A set is a collection which is both unordered and unindexed.

thisset = {"apple", "banana", "cherry"}

• Set items are unordered, unchangeable, and do not allow duplicate values.
• Unordered means that the items in a set do not have a defined order.
• Set items can appear in a different order every time you use them, and cannot be referred to by index or key.
• Sets are unchangeable, meaning that we cannot change the items after the set has been created.
• Duplicate values will be ignored.
• To determine how many items a set has, use the len() method.

thisset = {"apple", "banana", "cherry"}

print(len(thisset))

• Set items can be of any data type:

set1 = {"apple", "banana", "cherry"}
set2 = {1, 5, 7, 9, 3}
set3 = {True, False, False}
set4 = {"abc", 34, True, 40, "male"}

• It is also possible to use the set() constructor to make a set.

thisset = set(("apple", "banana", "cherry")) # note the double round-brackets

• frozenset() is just an immutable version of Set. While elements of a set can be modified at any time, elements of the frozen set remain the same after creation.

set1 = {"apple", "banana", "cherry"}
frzset=frozenset(set1)
print(frzset)

Dictionary

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• Dictionary is a collection which is unordered and changeable. No duplicate members.
• Dictionaries are used to store data values in key:value pairs.
• Dictionaries are written with curly brackets, and have keys and values:

thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}

• Dictionary items are presented in key:value pairs, and can be referred to by using the key name.

thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
print(thisdict["brand"])

• Dictionaries are changeable, meaning that we can change, add or remove items after the dictionary has been created.
• Dictionaries cannot have two items with the same key.
• Duplicate values will overwrite existing values.
• To determine how many items a dictionary has, use the len() function.

print(len(thisdict))

• The values in dictionary items can be of any data type

thisdict = {
  "brand": "Ford",
  "electric": False,
  "year": 1964,
  "colors": ["red", "white", "blue"]
}

• pop() Function is used to remove a specific value from a dictionary. You can only use key bot the value. Unlike Lists you have to give a value to this function

   car = {
    "brand": "Ford",
    "model": "Mustang",
    "year": 1964
  }
  
  x = car.pop("model")
  
  print(x)# Mustang
  print(car)#{'brand': 'Ford', 'year': 1964}
  

Conditional branching

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    if condition:
        pass
    elif condition2:
        pass
    else:
        pass

Loops

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Python has two primitive loop commands:

1. while loops
2. for loops

While loop

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• With the while loop we can execute a set of statements as long as a condition is true.
• Example: Print i as long as i is less than 6

i = 1
while i < 6:
  print(i)
  i += 1

• The while loop requires relevant variables to be ready, in this example we need to define an indexing variable, i, which we set to 1.
• With the break statement we can stop the loop even if the while condition is true
• With the continue statement we can stop the current iteration, and continue with the next.
• With the else statement we can run a block of code once when the condition no longer is true.

For loop

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• A for loop is used for iterating over a sequence (that is either a list, a tuple, a dictionary, a set, or a string).
• This is less like the for keyword in other programming languages, and works more like an iterator method as found in other object-orientated programming languages.
• With the for loop we can execute a set of statements, once for each item in a list, tuple, set etc.

fruits = ["apple", "banana", "cherry"]
for x in fruits:
  print(x)

• The for loop does not require an indexing variable to set beforehand.
• To loop through a set of code a specified number of times, we can use the range() function.
• The range() function returns a sequence of numbers, starting from 0 by default, and increments by 1 (by default), and ends at a specified number.
• 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).
• The else keyword in a for loop specifies a block of code to be executed when the loop is finished. 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)

• for loops cannot be empty, but if you for some reason have a for loop with no content, put in the pass statement to avoid getting an error.

for x in [0, 1, 2]:
  pass

Function definition

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def function_name():
    return

Function call

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function_name()

• We need not to specify the return type of the function.
• Functions by default return None
• We can return any datatype.