This is a guide on Python List comprehension. List comprehension is a great way to write simple and easy to read Python codes. You can use it dictionaries and sets as well.
Credits to Corey Schafer , creator of Python course materials.
lets create a list
num = range(10)
num
lets grab all the even numbers from that list
evens = []
for x in num:
if(x%2 == 0):
evens.append(x)
evens
lets use a list comperehension
evens2 = []
evens2 = [x for x in num if x%2 ==0]
evens2
lets to do a square of the even numbers
squaredEvens = [x**2 for x in num if x%2 == 0 and x >4]
squaredEvens
we can save it in a set form
squaredEvensSet = set([x**2 for x in num if x%2 == 0 and x >4])
squaredEvensSet
we can also use set in place of list in the for loop
squaredEvens1 = set([x**2 for x in squaredEvensSet if x%2 == 0 and x >4])
squaredEvens1
lets get letter , num pair for each letter in ‘abcd’ and number ‘0123’
my_list = []
for letter in 'abcd':
for num in range(4):
my_list.append((letter, num))
my_list
we can use list comprehension to achieve the same result
my_list2 = [(letter, num) for letter in 'abcd' for num in range(4)] #
my_list2
tne parameters in the tuple should be match the parameters in the for loop . that is letter, should match letter in for loop and num
should match num in for loop. you cannot have letter in tuple or let in for number. neither can you havve num in tuple and number in
for loop
We can also use list comprehension with dictionaries.
Lets create 2 lists and make a tuple of out it and then get a dictionary from the tuple
names= ['Bruce','Clark','Peter','Logan','Wade']
heroe = ['Batman','Superman','Spiderman','Wooverine','Deadpool']
#lets use a zip to turn these 2 lists into a tuple
zip(names, heroe)
Now with for loop we can get a dictionary of name being key and heroe being value
my_dict = {}
for name, hero in zip(names, heroe):
my_dict[name] = hero
my_dict
we can do the same thing using comprehension. hence dictionary comprehension
my_dict2 = {name: hero for name, hero in zip(names, heroe)}
my_dict2
We can add if clauses as usual
my_dict_if = {name: hero for name, hero in zip(names, heroe) if name != 'Peter'}
my_dict_if
A SET has UNIQUE VALUES
lets have list which has duplicates and add to a set and see how it behaves
nums3 = ['1','1','2','2','3','4','5','4','3','8','8','9','2']
#lets loop it through a for loop and add to a set.
myset = set()
for n in nums3:
myset.add(n)
myset
it returns only uniques values as SETS only contain unique values
We can accomplish the same thing with SET comprehension which also takes a curly bracket
myset2 = {n for n in nums3}#
myset2
GENERATORS. they are very similar to list comprehension but they USE PARENTHESIS ie ()
and the results can be iterated through
Lets look at one quick example
We want to get n*n for each n in nums
nums_gen = [1,5,2,5,2,6,2,86,5,2,8,2]
def gen_func(num):
for n in nums:
yield n*n
my_gen = gen_func(nums_gen)
#my_gen
lets get the values from my_gen
for i in my_gen:
print(i)
We can do the same thing with GENERATOR
my_gen2 = (n*n for n in nums_gen)
now lets iterate through my_gen2
for y in my_gen2:
print(y)
