Python#04

Comprehension 

• A compact way of creating a Python data structure from iterators.

• With comprehensions, you can combine loops and conditional tests with a less verbose syntax.

• Comprehension is considered more Pythonic and often useful in a variety of scenarios.

List comprehension is a way to build a new list by applying an expression to each item in an iterable.

Basic Example

Suppose you want to create a list of all integer square numbers from 0 to 4. You could build that list by appending one item at a time to an empty list:

ilist = []
ilist.append('a')
ilist.append(1)
ilist.append(4)
ilist.append(9)
ilist.append(16)
print(ilist)
# Prints ['a', 1, 4, 9, 16]

Using range() function, the above can be done:

alist = []
for x in range(5):
    alist.append(x*x)
print(alist)
# Prints [0, 1, 4, 9, 16]

The following examples are self explanatory 

# lambda functions

#ex 1
print(50*'_','Iteration using normal for loop')

alist = []

for x in range(5):

    alist.append(x*x)

print(alist)

# Prints [0, 1, 4, 9, 16]


#ex 2 Single line Comprehensive code

print(50*'_','Iteration using Single line code')

alist= [i*i for i in range(0,5)]

print(alist)

#Prints [0, 1, 4, 9, 16]

# ex 3 Please note the print values using lambda alone  , def() and lambda and map
def square(i):

    return i * i

avalue = lambda x: x * x

print(50*',','using lambda and def() ')

print(avalue(5))

# Prints 25

print(square(5))

#Prints 25


#ex4 using lambda and map function
print(50*'-','using lambda & map ')


alist = list(map(lambda i: i*i, [i for i in range(1,6)]))

print(alist)

#Prints [1, 4, 9, 16, 25]


#ex5 using lambda and filter function

print(50*'-','using lambda & filter ')

ilist = [1,2,3,4,5,7,8,9,10]

flist = filter (lambda x: x > 3, ilist)

print(list(flist))

#Prints [4, 5, 7, 8, 9, 10]

#ex6 lambda and reduce function
print(50*'-','using lambda & reduce ')

# importing functools for reduce()

import functools

# initializing list
ilist = [1, 2, 3, 4, 5]

# to compute product of the list
print("The product of the list elements is : ", end="")

print(functools.reduce(lambda a, b: a * b, ilist))
# Prints:The product of the list elements is : 120

# to compute maximum element from list
print("The maximum element value in the list is : ", end="")

print(functools.reduce(lambda a, b: a if a > b else b, ilist))
# Prints  The maximum element value in the list is : 5

Results : 

__________________________________________________ Iteration using normal for loop
[0, 1, 4, 9, 16]
__________________________________________________ Iteration using Single line code
[0, 1, 4, 9, 16]
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, using lambda and def() 
25
25
-------------------------------------------------- using lambda & map 
[1, 4, 9, 16, 25]
-------------------------------------------------- using lambda & filter 
[4, 5, 7, 8, 9, 10]
-------------------------------------------------- using lambda & reduce 
The product of the list elements is : 120
The maximum element value in the list is : 5

Ex 4,5,6 explains the lambda function usage.

Happy Learning, 👨👩👫