This is a living post where I document and share all the python one line code blocks. When switching between languages I feel like these are the first things I forget.
The solution I found was to have a kind of scrap book of examples where I can quickly look up examples. That's what this post is about. Where possible I also comment on use and performance.
List comprehension and variants
This is the mother of all python one-liners. Iterating through a list, creating a new list in a single line.
l = [1,3,5,7]
double_list = [num * 2 for num in l]
This defines a new list double_list where each element of the original list is multiplied by 2.
Set comprehension
Changing the outer brackets and the above can be turned into a set.
l = [1,3,5,5,7]
double_set = {num * 2 for num in l}
The example creates double_set an object with 4 elements {2,6,10,14}.
Dictionary comprehension
Similarly we can create a new dictionary in the form of a comprehension using the syntax below.
l = [1,3,5,5,7]
double_dict = {num:num * 2 for num in l}
This will return a dictionary of the form {1: 2, 3: 6, 5: 10, 7: 14}
Generator comprehension
A final example we can create a generator for immediate use by using parenthesis enclosing the comprehension.
l = [1,3,5,5,7]
double_gen = (num * 2 for num in l)
double_gen.__next__()
This will return 2 from the call to the __next__() element in the generator. The Python documentation gives the following use case where a generator is passed to sum() instead of creating a list first.
sum(i*i for i in range(10))
One line conditionals
Classic one line conditional is a single line if-else statement as below.
meaning_of_everything = 42
is_meaning_of_everything = True if meaning_of_everything == 42 else False
if-else statements can be combined with one line comprehensions in the following format.
odds = [i for i in range(10) if i % 2 == 1]
The above will output odd values only [1, 3, 5, 7, 9].
Functional arguments
When declaring a function using the *args and **kwargs syntax allows passing a list or dictionary of arguments to a function. What if we want to do the opposite? for example we have a list or a dictionary that we want to expand into *args or ***kwargs.
- Expanding a list of arguments:
function(*alist) - Expanding a dictionary of keyword arguments:
function(**adict)