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Some Helpful Tricks

Some Helpful Tricks

In this lesson, we'll see some useful Pythonic tricks.

List Comprehension

The list comprehension is a well-known python construct. Here are some tricks with a list in Python:

List Initialization of Size N

Here is to initialize a list of size ‘N’ in Pythonic way:

Python 3.5
lst = [0] * 5  # A list of size 5 initialized with zeros.
print(lst)

filter Function

If the problem is similar to find positive integers then instead of writing:


for x in lst:
    if x % 2 is 0:
        print(x)

We can use filter and lambda functions as follows:

Python 3.5
# A list contains both even and odd numbers.  
seq = [0, 1, 2, 3, 5, 8, 13] 
  
# result contains odd numbers of the list 
result = filter(lambda x: x % 2, seq) 
print(list(result))

map function

If the problem is similar to double all integers in a list then instead of writing:


for x in range(len(lst)):
    lst[i] = lst[i] + lst[i]

We can use map and lambda functions as follows:

Python 3.5
# Double all numbers using map and lambda 
  
numbers = (1, 2, 3, 4)
result = map(lambda x: x + x, numbers) 
print(list(result))

in Operator

If the problem is similar to find something in a list then instead of writing:


for i in range(len(lst)):
    if lst[i] == number:
        print("True")

We can use in operator as follows:

Python 3.5
number = 3
found = number in [1, 2, 3, 4, 5]
print(found)

enumerate Function

In scenarios where you may want to access the index of each element in a list, it’s better you employ the enumerate function instead of:


lst = list(range(10))
index = 0
while index < len(lst):
    print(lst[index], index)
    index += 1
Python 3.5
lst = list(range(5))
for index, value in enumerate(lst):
  print(value, index)

Dictionary Comprehension

Dict Comprehension’s purpose is similar to construct a dictionary using a well-understood comprehension syntax.

Bad:

emails = {}
for user in users:
    if user.email:
        emails[user.name] = user.email

We can replace the above code with this neat code:

Python 3.5
emails = {user.name: user.email for user in users if user.email}

Set Comprehension

The set comprehension syntax is relatively new and often overlooked. Just as lists, sets can also be generated using a comprehension syntax.

Bad:

elements = [1, 3, 5, 2, 3, 7, 9, 2, 7]
unique_elements = set()

for element in elements:
    unique_elements.add(element)
print(unique_elements)

We can replace the above code with this neat code:

Python 3.5
elements = [1, 3, 5, 2, 3, 7, 9, 2, 7]
unique_elements = {element for element in elements}
print(unique_elements)

Unnecessary Repetition

We can avoid unnecessary repeated lines in Python. Suppose if we want to print:

print('------------------------------')
print("Educative")
print('------------------------------')

The above code can be replaced with:

Python 3.5
print('{0}\n{1}\n{0}'.format('-'*30, "Educative"))