Python One-Liners

 January 20, 2021      Stardate: 74520.4     Tagged as: Python

As a bonus, here are two of my favorite python one-liners:

Swapping Variables - no need to use temp variables. In some other languages, like C, you would need a temporary variable to hold a value while you swap them around. Something like this:

double a, b, temp;

// Assign values to variables
a = 5;
b = 7;

// Value of first variable is assigned to temp
temp = a;

// Value of second variable is assigned to the first
a = b;

// Value of temp (initial first) is assigned back to the second variable
b = temp;

But in Python it’s a lot more… elegant.

# Assign values to variables
a, b = 5, 7

# Swap values
a, b = b, a

Multiple Variable Assignment - the above example shows another of my favorites. We can assign values to multiple variables with a single line. Even cooler is we can use an asterix and assign multiple values to a variable.

a, *b = [1, 2, 3, 4, 5]
print(a, b)

> 1 [2, 3, 4, 5]

In the above code, a is assigned the first element in the list while b is assigned all the remaining.

*a, b = [1, 2, 3, 4, 5]
print(a, b)

> [1, 2, 3, 4] 5

In the above code, a is assigned all the elements except the last, and b is assigned the last element in the list.

a, *b, c = [1, 2, 3, 4, 5]
print(a, b, c)

> 1 [2, 3, 4] 5

Finally, in the above code, a is assigned the first element, c is assigned the last element, and b is assigned all the elements in between.

List Comprehension - this is a really cool way to build a list without using loops. I’ve seen people go overboard on it where I couldn’t even understand what was going on. Here is the basic example:

# Silly loop example
my_list = []
for i in range(5):
    my_list.append(i)
    
# List comprehension
my_list = [i for i in range(5)]

Here is the syntax:

[expression for item in iterable if condition == True]

so in the previous example,

my_list = [i<expression> for i<item> in range(5)<iterable>]

You can also get complex with the expression,

some_array = [True, False, True]
my_list = ["Hello" if i else "Goodbye" for i in some_array]
print(my_list)

> ['Hello', 'Goodbye', 'Hello']

In a previous post I did a multi-line if/elif/else replacement:

# Loop
for i in range(1, 101):
    if (i%3==0 and i%5==0): print("FizzBuzz")
    elif i%3==0: print("Fizz")
    elif i%5==0: print("Buzz")
    else: print(i)
        
# List Comprehension
[ 'FizzBuzz' if (i%3==0 and i%5==0) else 'Fizz' if i%3==0 else 'Buzz' if i%5==0 else i for i in range(1, 101) ]

Cool, huh?