Basics of Python

Jalaz Kumar · December 15, 2020

Python   Core

Python is a popular programming language. Created by Guido van Rossum (1991).

Used for:

  • web development (server-side) (flask, pjango)
  • software development (pyqt5, tkinter)
  • mathematics (numpy, scipy)
  • scripting
  • data science (pandas, sklearn, tensorflow)

Simple Syntax. Interpreted language. Can be treated in procedural way, object-oriented way and functional way.

Basics of Python

Comments

# Single line comments
'''
Multi
line
comment
'''

Variables

  • No separate command of declaring variables.
  • No need to specify datatype of variable.
  • For specifying datatype, casting is used.
  • type() is used for getting the datatype of variable.

Built-in datatype

built-in-datatype

Conditionals & Iterations

if-elif-else blocks

sp=1500
cp=1200
if(sp>cp):
	print("Profit of",sp-cp)
elif(cp>sp):
	print("Loss of",cp-sp)
else:
	print("equal equal")

taking input & for loop

count=0
print("Input your name")
name = input()
for letter in name:
	if letter in ['A','E','I','O','U','a','e','i','o','u']:
		count = count +1
print("You have",count,"Vowels in name")

while loop

var=1
while(var<=10):
	print(var)
	var =var+1

break & continue

for var1 in range(1,15):
	if var1 in range(5,8):
		continue
	elif var1 in [0,14]:
		break
	else:
		print(var1)

pass

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

Collections

4 built-in datatypes for storing collections of data.

list tuple set dictionary
ordered ordered unordered unordered
changeable unchangeable unchangeable changeable
indexed indexed unindexed  
duplicate items allowed duplicate items allowed no duplicate items allowed no duplicate items allowed
created using square brackets created using round brackets written with curly brackets written with curly brackets

list

listJK = ["mcat-search", "product-search", "bl-search", "group-search", "auto-suggest"]
print(listJK)
print(listJK[0])

len(listJK)

complexList = ["abc", 34, True, 40, "male"]			# Different datatypes can be part of list

listFruits = list(("apple", "banana", "cherry")) # Creation using constructor
print(listFruits)

if "apple" in listFruits:
	print("In OP usage")

listFruits[1] = "orange"					  # Changing Allowed
listFruits.insert(1, "banana")				# Insertion at any position Allowed
listFruits.append("melon")				    # Addition Allowed

listCompanies = ["google", "facebook", "amazon"]
listNew = ["netflix", "microsoft"]
listCompanies.extend(listNew)

listFruits.remove("apple")
listFruits.pop(2)								# Removes the specified indexed element
listFruits.pop()								# Removes the last indexed element

listCompanies.clear()						# Empties the list

List Comprehension & looping

newlist = [expression for item in iterable if condition == True]

newlist = [x.upper() for x in fruits if x in ["apple", "banana", "cherry"]]

for company in listCompanies:
  print(company)

for i in range(len(listCompanies)):
	print(listCompanies[i])

i = 0
while(i<len(listCompanies)):
	print(listCompanies[i])
	i = i+1

list-methods

tuple

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

tupleJK = tuple(("apple", "banana", "cherry")) 			# Creation using constructor
print(tupleJK)

# Tuples are unchangeable, meaing that you cannot change, add, or remove items once the tuple is created.
# Work-around for this is: tuple -> list -> {modify} -> tuple

y = list(tupleJK)
y.remove("apple")
y[0] = "orange"
y.append("melon")
tupleJK = tuple(y)

# Unpacking tuples
fruits = ("apple", "banana", "cherry", "strawberry", "raspberry")
(green, yellow, *red) = fruits

tuple-methods

set

setJK = {"c", "java", "python"}
print(setJK)
len(setJK)

setJK = set(("apple", "banana", "cherry")) 			# Creation using constructor

setJK.add("orange")

setJK.remove("banana")				# Raises error if item to remove doesn't exist
setJK.discard("banana")				# Doesn't raises error if item to remove doesn't exist

tropicalFruits = {"melon", "apricot"}
setJK.update(tropicalFruits)			# Adding a python collections into set

setNew = setJK.union(tropicalFruits)		# Joining sets using union op

set-methods

dict

  • Stores data values in key-value pairs
  • value of dictionary items can be of any datatype & are referred using the keys.
dictJK =	{ "brand": "Ford", "model": "Mustang", "year": 1964 }
brand = dictJK["brand"]
brand = dictJK.get("brand")

len(dictJK)

keyDictJK = dictJK.keys()
valueDictJK = dictJK.values()
itemsDictJK = dictJK.items()				# Tuple of items

# All these 3 are views of dictionary, any modifications in dictionary are reflected in these lists.

if "model" in dictJK:
	print("key is present")

dictJK["year"] = 1987
dictJK.update({"year": 1987})

dictJK["color"] = "Red"
dictJK.update({"color": "Red"})

dictJK.pop("model")

dictJK.clear()

# Looping Dictionaries

for x in dictJK:
	print(x)
	print(dictJK[x])

for x in dictJK.keys():
	print(dictJK[x])

for x,y in dictJK.items():
	print(x,y)

# Copying Dictionaries

dict1 = dict2			# Only references, softcopy is created
dict1 = dict2.copy()		# WA 1
dict1 = dict(dict2)			# WA 2

dict-methods

String Ops

name = "Jalaz Kumar"
print(name)
print(name[1])

for x in name:
	print(x)

len(name)

# Slicing
print(name[3:])
print(name[:4])
print(name[1:4])

m1Name = name.lower()
m2Name = name.upper()
m3Name = name.replace('J','K')

print(name.split())

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

myorder = "I want to pay {2} dollars for {0} pieces of item {1}."
print(myorder.format(10, 75655, 23))

There are several other important methods:

  • capitalize()
  • count()
  • encode()
  • find()
  • isdigit()
  • join()
  • split()
  • strip()
  • title()
  • swapcase()

Functions

  • Simple arguments
def Summation(a,b):
	val = a+b
	return val

result = Summation(3,4)
  • Arbitrary arguments (*args)
    • Any number of arguments as function parameters
def variableFunc(*params):
	for var in params:
		print(var)
	return

variableFunc(10,20,True,"Hello")
  • Keyword arguments
    • arguments in the form of key-value pair
    • ordering of arguments doesn’t matter
def calcMarks(maths, physics, chemistry):
	return maths+physics+chemistry

calcMarks(chemistry=95, maths=98, physics=96)
  • Keyword Arbitrary arguments
    • any number of keyword arguments as function parameters
def results(**requestparams):
	if "result_count" in requestparams:
		blah blah blah

results(result_url="kw-mapping", result_count="189")
  • Default parameters
def getNation(country = "india"):
	print("My nation is "+country)

getNation("nepal")
getNation()
getNation("britain")
  • Python lambda
    • lambda is a small anonymous function
    • can take any number of arguments, but can have only 1 expression
product = lambda a,b:a*b
print("Result:",product(12,5))
  • power of lambda is shown when used inside another function
def myfunc(n):
  	return lambda a : a * n

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

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

Python OOPs

  • Is an object-oriented programming language
  • Almost everything in Python is an object, with its properties and methods.

__init__()

  • built-in function called implictly when the object is created.
  • used as initializer
  • behaves in similar manner as constructors of java/c++ but is not. (__new__() & __init__() combinely acts as constructor)

self

  • refers to the current instance of the class
  • used for accessing the class variables & functions
  • has to be always the first parameter of the functions
class Person:
	def __init__(self, name, age):
		self.name = name
		self.age = age

	def printName(self):
		print("Hello, my name is " + self.name)

p1 = Person("Jalaz", 25)
print(p1.name)
print(p1.age)
p1.printName()

Inheritence

class Person:
	def __init__(self, name):
		self.name = name

	def printName(self):
		print("Hello, my name is " + self.name)

class Student(Person):
	def __init__(self, name, class):
		Person.__init__(self, name)
		self.class = class

	def printClass(self):
		print("Class is "+ self.class)

s1 = Student("Jalaz", "5th year")
s1.printName()												# Call to the parent class' function
s1.printClass()												# Call to the child class' function

super()

  • can also be used in child class’ __init__() for initialising parent class’ variables.
  • Person.__init__() can be replaced with super().__init__()

Python Exception Handling

  • try : lets us test a block of code for errors.
  • except : lets us handle the error.
  • finally : lets us execute code either from try/except.
try:
  f = open("demo.txt")
  f.write("This is Jalaz")
except:
  print("Issue occured while writing")
finally:
  f.close()
  • raise : we can choose to throw an exception if a condition occurs.
x = -1

if x < 0:
  raise Exception("Sorry, no numbers below zero")

Python File I/O

Data/binary file

  • open(), close(), read(), readline() & write() are few important functions.
  • 4 major modes of operations:
    • “w” - write - overwrites existing content
    • “r” - read - reads the existing content
    • “a” - append - appends to the existing content
    • “x” - create - create a file
f = open("/data/tech/jalaz.txt", "r")
f.read()
f.readline()

for line in f:
	print(line)
f.close()

f = open("/data/tech/jalaz.txt", "w")
f.write("yes, this is second line")
f.close()

JSON file

import json

jsonString =  '{ "name":"Jalaz", "age":25, "company":"IndiaMART" }'
pyDict = json.loads(jsonString)
print(pyDict["age"])

jsonString = json.dumps(pyDict)
print(jsonString)
print(json.dumps(pyDict, indent=4))

CSV file

  • pandas is a really good library for csv stuff in python
import pandas as pd

df = pd.read_csv('/data/tech/data_ip.csv')
print(df)

df.to_csv('/data/tech/data_op.csv')

Additional supports

Date

import datetime

x = datetime.datetime.now()
print(x.year)							   			# 1997
print(x.month)										  # 8
print(x.strftime("%x")) 								# 8/12/1997

Math

print(pow(4, 3))						# Built-in math functions
print(abs(6.4))

import math
print(math.sqrt(64))					# Ships with math module
print(math.pi)

RegEx

import re

text = "IndiaMART is an Indian company"

print(re.findall("India", text))								# ['India', 'India']

x = re.search("\s", text)												# Match object is returned
print("Position of first whitespace:", x.start())

print(re.sub("India", "Australia", text))        # AustraliaMART is an Australian company
print(re.sub("India", "Australia", text, 1))		# AustraliaMART is an Indian company

Important Scripts

  • Hitting & Receiving response from external API
import urllib.request as urllib2
import json

def getServiceResults(searchKeyword):
	serviceUrl = "http://"+"<IP>"+":"+"<PORT>"+"/<ENDPOINT>?source="+"dir.search"+"&q="+urllib2.quote(searchKeyword)
	connection = urllib2.urlopen(serviceUrl)
	response = json.load(connection)

	return response['results'][0]
  • Reading keywords from file
def extractKeywords(keywordsFile):
    fileObject = open("/data/tech/keywords/"+keywordsFile, "r")
    keywords = []
    for line in fileObject:
        keywords.append(line.split('\n')[0])
    fileObject.close()

    return keywords
  • Gathering data from an external API call for keywords
keywords = extractKeywords("keywords_100")
fileOBJ = open("/data/tech/results/"+resultsFile, "w")
for keyword in keywords:
    print(keyword)
    fileOBJ.write(str(keyword))
    fileOBJ.write(getServiceResults(server,port,source,keyword,fileOBJ))
    fileOBJ.write(str("\n"))
    fileOBJ.flush()
fileOBJ.close()
print("\n\n-------------------------\nDone!")
  • Reading CLI arguments
def readCLIArguments():
    argumentList = sys.argv
    Parameters = {}
    Parameters["source"] = argumentList[1]
    keywordsFile = argumentList[2]
    Parameters["keywords"] = extractKeywords(keywordsFile)

    return Parameters
  • Scrapping data from Oracle DB

Twitter, Facebook