Python - Virtual env, pip freeze, Lambda function, join method, format method and map, filter, reduce

 Virtual Env:

An environment which is same as the system interpreter but is isolated from the other python environments on the system.

Installation:

to use virtual environment:

    pip install virtualenv

to create:

    virtualenv myprojectenv

to activate:

    activate

pip freeze:

It returns all the packages installed in a given env along with the versions.

    pip freeze > list.txt

we can share the this file to other user and they can recreate the same env using:

    pip install -r list.txt

Lambda function:

syntax:

    lambda arguments: expressions

instance:

    square = lambda a : a * a

    square(2) 

Join method:

It creates a string from iterable objects.

l=["apple","mango","banana"]

" and ".join(l)

output: "apple and mango and banana"

format method:

formats the values inside a string into a desired output.

template.format(arguments)

example:

"{} is a good {}".format("john","boy")

or

"{1} is a good {0}".format("boy","john")

output: john is a good boy

Map, filter and reduce:

Map:

map applies a function to all the items in a input list.

map(function,list)

Filter:

It creates a list of items for which the function returns true.

list(filter(function,list))

Reduce:

It applies a rolling computation to sequential pair of elements.

from functools import reduce

val=reduce(function, list)

if the function computes the sum of two numbers and the list is [1,2,3,4], the output will be 10.

Practice:

Create two virtual environments , install few packages in the first one. create a similar env in the 2nd one.

pip install virtualenv

virtualenv env1

virtualenv env2

.\env1\Scripts\activate.ps1

pip install pandas

pip freeze > 2.txt

deactivate

 .\env2\Scripts\activate.ps1

pip install -r .\2.txt

deactivate

WAP to input name, marks and phone numbers of a student and format it using the format function like "The name of the student is Sri and his marks are 65 and phone number is 0000000000.

name= input("Please enter your name: ")

marks= input("Please enter your marks: ")

phone= input("Please enter phone number: ")

template="the name of the Stdent is {} and his marks are {} and his phone number is {}."

print(template.format(name,marks,phone))

a list contains the multiplication table of 7. WAP to convert to a vertical string of the same numbers.

num = int(input("Enter a number: "))

table = [str(num * i) for i in range(1,11)]

print(table)

vertical="\n".join(table)

print(vertical)

WAP to filter a list of numbers which are divisible by 5.

myList=[1,2,4,6,7,8,9,123,54,67,90,45,5,56,50]

newList=filter(lambda a:a % 5 ==0,myList)

print(list(newList))

WAP to find the max of the numbers in a list using reduce function.

from functools import reduce

numberList=[1,2,4,6,7,8,9,123,54,67,90,45,5,56,50]

maxnumber=reduce(max,numberList)

print(maxnumber)