Python

Introduction

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>

Create and execute a program

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

Basic Datatypes

Data Type	Description
`int`	Integer values [0, 1, -2, 3]
`float`	Floating point values [0.1, 4.532, -5.092]
`char`	Characters [a, b, @, !, `]
`str`	Strings [abc, AbC, A@B, sd!, `asa]
`bool`	Boolean Values [True, False]
`complex`	Complex numbers [2+3j, 4-1j]

Keywords

As of python3.8 there are 35 keywords:

Keyword	Description	Category
`True`	Boolean value for not False or 1	Value Keyword
`False`	Boolean Value for not True or 0	Value Keyword
`None`	No Value	Value keyword
`and`	returns true if both (oprand) are true (other language `&&` )	Operator keyword
`or`	returns true of either operands is true (other language `\|\|` )	Operator keyword
`in`	returns true if word is in iterator	Operator keyword
`is`	returns true if id of variables are same	Operator keyword
`not`	returns opposite Boolean value	Operator Keyword
`if`	get into block if expression is true	conditional
`elif`	for more than 1 if checks	conditional
`else`	this block will be executed if condition is false	conditional
`for`	used for looping	iteration
`while`	used for looping	iteration
`break`	get out of loop	iteration
`continue`	skip for specific condition	iteration
`def`	make user defined function	structure
`class`	make user defined classes	structure
`lambda`	make anonymous function	structure
`with`	execute code within context manager’s scope	structure
`as`	alias for something	structure
`pass`	used for making empty structures(declaration)	structure
`return`	get value(s) from function, get out of function	returning keyword
`yield`	yields values instead of returning (are called generators)	returning keyword
`import`	import libraries/modules/packages	import
`from`	import specific function/classes from modules/packages	import
`try`	this block will be tried to get executed	execption handling
`execpt`	is any execption/error has occured it’ll be executed	execption handling
`finally`	It’ll be executed no matter execption occurs or not	execption handling
`raise`	throws any specific error/execption	execption handling
`assert`	throws an AssertionError if condition is false	execption handling
`async`	used to define asynchronous functions/co-routines	asynchronous programming
`await`	used to specify a point when control is taken back	asynchronous programming
`del`	deletes/unsets any user defined data	variable handling
`global`	used to access variables defined outsied of function	variable handling
`nonlocal`	modify variables from different scopes	variable handling

Operators

Operator	Description
`( )`	grouping parenthesis, function call, tuple declaration
`[ ]`	array indexing, also declaring lists etc.
`!`	relational not, complement, `!` a yields true or false
`*`	multiply, `a * b`
`/`	divide, `a / b`
`%`	modulo, `a % b`
`+`	add, `a + b`
`-`	subtract, `a - b`
`<<`	shift left, left operand is shifted left by right operand bits (multiply by 2)
`>>`	shift right, left operand is shifted right by right operand bits (divide by 2)
`<`	less than, result is true or false, `a < b`
`<=`	less than or equal, result is true or false, `a <= b`
`>`	greater than, result is true or false, `a > b`
`>=`	greater than or equal, result is true or false, `a >= b`
`==`	equal, result is true or false, `a == b`
`!=`	not equal, result is true or false, `a != b`
`&`	bitwise and, `a & b`
`^`	bitwise exclusive or XOR, `a ^ b`
`\|`	bitwise or, `a \| b`
`&&`, `and`	relational and, result is true or false, `a < b && c >= d`
`\|\|`, `or`	relational or, result is true or false, `a < b \|\| c >= d`
`=`	store or assignment
`+=`	add and store
`-=`	subtract and store
`*=`	multiply and store
`/=`	divide and store
`%=`	modulo and store
`<<=`	shift left and store
`>>=`	shift right and store
`,`	separator as in `( y=x,z=++x )`
`~`	bitwise not, ones complement, `~a`
`-`	unary minus, `- a`
`+`	unary plus, `+ a`
`&=`	bitwise and and store
`^=`	bitwise exclusive or and store
`\|=`	bitwise or and store

Basic Data Structures

List

List is a collection which is ordered and changeable. Allows duplicate members.

Syntax:

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

Tuple

Tuple is a collection which is ordered and unchangeable. Allows duplicate members.
A tuple is a collection which is ordered and unchangeable.

Syntax:

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

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

Dictionary

Dictionary is a collection which is unordered and changeable. No duplicate members.
Dictionaries are used to store data values in key:value pairs.

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"]
}

Flow Control

Conditional

    if condition:
        <commands>
    elif condition2:
        <commands>
    else:
        <commands>

Loops

For loop

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(b,e,i) function returns a sequence of numbers, starting from b (0 as default), and increments by i (1 by default), and ends at number e.
- 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)

While loop

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.

Functions

Definition

def function_name():
    return

Call

function_name()

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