List Comprehensions
Python has a really cool feature known as comprehensions. Below are a few examples of how this might work with lists. They can also be implemented for dictionaries as well.
Say we want to create a list of characters that are part of a string containing a phrase. Traditionally, we would approach that problem like this:
characters = []
phrase = “Python 3!”
for character in phrase:
characters.append(character)
print(characters)
But with list comprehension, it can be reduced to this:
characters = [character for character in phrase]
print(characters)
Output is the same for both:
[‘P’, ‘y’, ‘t’, ‘h’, ‘o’, ‘n’, ‘ ‘, ‘3’, ‘!’]
[‘P’, ‘y’, ‘t’, ‘h’, ‘o’, ‘n’, ‘ ‘, ‘3’, ‘!’]
To help remember how to implement a list comprehension, always think “[new_item for item in list]”. But we can also have a condition with a list comprehension. Lets say we want to convert names to all upper case, but only if they have more than 4 characters in them. Below is how to accomplish that with a list comprehension.
names = [“Bill”, “Maria”, “Christopher”, “Sam”]
new_names = [name.upper() for name in names if len(name) > 4]
print(new_names)
Output:
[‘MARIA’, ‘CHRISTOPHER’]