Python Tutorials part I Getting Started

4 minute read

By: Vishnu Prakash Singh

01 Oct,2019

from IPython.display import Image;from datetime import date
from IPython.core.interactiveshell import InteractiveShell
InteractiveShell.ast_node_interactivity = "all"

About Python-

Created By Guido Van Rossum
First released in 1991
Interpreted, high-level, general-purpose programming language
Purpose: build anything
It is Open Source
Python Packages like numpy, pandas, scikit learn available for Data Science

Installing Python

click here for win32; click here for win64

Image('inst_py.png',width=400,height = 200)

png

Important python libraries for data science

Numpy
- For scientific computing with Python
Pandas
- Provides various high level convenient data structures, functions, and classes
Matplotlib
- For data visualization
Scikit learn
- Machine learning library for the Python programming language.

Image('python-lib.png',width=400,height = 200)

png

Expressions in Python

In python, 2 + 3 is an example of basic expression
Expression has values & operators
Expressions always reduce down to a single value
The operators and values are put together as per python rules
The values in an expression can have various data types

Math Operators from Highest to Lowest Precedence

Operator	Operation	Example	Evaluates to…
**	Exponent	2**3	8
%	Modulus/remainder	23%6	5
//	Integer division	23//6	3
/	Division	23/6	3.83
*	Multiplication	2*6	12
-	Subtraction	6-2	4
+	Addition	6+2	8

Common Data Types

Data type	Examples
Integers	-1, -2, 0 , 1, 3 , 5
Floating-point numbers	-1.34, -1.0, 0.0, 3.45
Strings	Hello’, ‘PYTHON’, ‘LeArN’
Bool	True , False

Data Structures and Sequences

List
Dictionary
Tuple
Numpy Array

List

Contains multiple values in an ordered sequence.
Can be stored in a variable or passed to a function.
Values inside lists are called items.
Items in a list are separated by comma and can have different data types.
e.g. list1 = [ 'abc', 1, 1.50, True ]
Items of a list can be accessed using index starting from 0.
Basic operations on list are as follows

Accessing elements of list

list1 = [ 'abc', 1, 1.50, True ]

print('Length of list is ' + str(len(list1)))
print('First item of list is ' + str(list1[0]))
print('Last item of list is ' + str(list1[-1]))
print('First 2 items of list are ' + str(list1[0:2]))
print('Last 2 items of list are ' + str(list1[-2:]))

Length of list is 4
First item of list is abc
Last item of list is True
First 2 items of list are [‘abc’, 1]
Last 2 items of list are [1.5, True]

Updating list

list1[0] = 'xyz'
print('New list is ' + str(list1))
list1[-1] = 'False'
print('New list is ' + str(list1))

New list is [‘xyz’, 1, 1.5, True]
New list is [‘xyz’, 1, 1.5, ‘False’]

List Concatenation and List Replication

list2 = ['A', 'B', 'C']
list3 = list1 + list2
print('Concatenated list is ' + str(list3))
print('Replicating list2 twice ' + str(list2*2))

Concatenated list is [‘xyz’, 1, 1.5, ‘False’, ‘A’, ‘B’, ‘C’]
Replicating list2 twice [‘A’, ‘B’, ‘C’, ‘A’, ‘B’, ‘C’]

list1
list2

[‘xyz’, 1, 1.5, ‘False’]
[‘A’, ‘B’, ‘C’]

# appending value to list
list4 = [1,3,'v',True]
list4.append('X')
print('Appended List is ' + str(list4))

Replicating list2 twice [1, 3, ‘v’, True, ‘X’]

# Extending list
list4 = [1,3,'v',True]
list5 = [2,'s',False]
list4.append(list5)
print('Extended List is ' + str(list4))

Extended List is [1, 3, ‘v’, True, [2, ‘s’, False]]

# Inserting value in a list
list4 = [1,3,'v',True]
list4.insert(2,'C')
print('Updated list after inserting "C" at 2nd index ' + str(list4))

Updated list after inserting “C” at 2nd index [1, 3, [‘C’, 3], ‘v’, True]

# Removing value in a list
list4 = [1,3,'v',True]
list4.remove('v')
print('Updated list after removing "v" is ' + str(list4))

Updated list after removing “v” is [1, 3, True]

# Popping value in a list
list4 = [1,3,'v',True]
list4.pop(1)
print('Updated list after removing item at 1st index ' + str(list4))

3
Updated list after removing item at 1st index [1, ‘v’, True]

# Index, count, reverse functions
list6 = ['A', 'B', 'C', 'A', 'A']
print('Index of element "B" is ' + str(list6.index('B')))
print('Count of element "A" is ' + str(list6.count('A')))
print('Reversed list is ' + str(list6.reverse()))

Index of element “B” is 1
Count of element “A” is 3
Reversed list is None

Dictionary

dict = {'key1' : 'value1', 'key2' : 'value2' }
The items are separated by commas, and the whole thing is enclosed in curly braces
Keys are unique within a dictionary while values may not be.
The values of a dictionary can be of any type
the keys must be of an immutable data type such as strings, numbers, or tuples
example of dict - dict = {'Name': 'Bank', 'Age': 20, 'Class': 'First'}

dict1 = {'Name': 'Bank', 'Age': 20, 'Class': 'First'}
dict1.items()
dict1.keys()
dict1.values()

‘Bank’
dict_items([(‘Name’, ‘Bank’), (‘Age’, 20), (‘Class’, ‘First’)])
dict_keys([‘Name’, ‘Age’, ‘Class’])
dict_values([‘Bank’, 20, ‘First’])

# accessing values of dictionary
dict1['Name']
dict1.get('Age')

‘Bank’
20

# dictionary within dictionary
dict2={"child1": {"name":"x","age":5},"child2": {"name":"y","age":15}}
dict2['child1']['name']
dict2['child2']['age']

‘x’
15

# inversing a dict using dict comprehension
inv_dict1 = {val: key for key, val in dict1.items()}
inv_dict1

{‘Bank’: ‘Name’, 20: ‘Age’, ‘First’: ‘Class’}

Tuple

A tuple is a sequence of immutable Python objects
Tuples are sequences, just like lists
The tuples cannot be changed unlike lists
Tuples use parentheses, whereas lists use square brackets
Tuples items can be accessed in the same way as lists
The operations on tuples are same as of list.
examples of tuple - tuple = (12, 34.56, 'X')

Loops in Python

IF ELSE Loop

today = input()  #'monday'
if today=='saturday':
    print('Today is saturday')
elif today == 'monday':
    print('Today is monday')
else:
    print('Today is neither monday nor saturday')

sunday
Today is neither monday nor saturday

For loop

for color in ['blue', 'orange', 'red', 'black']:
    print(color)

blue
orange
red
black

lst = [1,2,3,4,5]
lst_sqr = []
for i in range(len(lst)):
    lst_sqr.append(lst[i]*lst[i])
lst_sqr

[1, 4, 9, 16, 25]

using list comprehension

[i*i for i in lst]