Welcome to part five of our Python 3 features series! Today we’re looking at f-strings, cool numeric literal tricks, and a bit of extra syntax sugar that makes Python code a joy to write.

Before f-strings (Python 3.6+), we had % formatting and str.format(), which can feel clunky:

name = 'Alice'
age = 30
# Old ways:
print('Hello, %s! You are %d.' % (name, age))
print('Hello, {}! You are {}.'.format(name, age))

With f-strings, just put an f before the quote and embed expressions directly:

print(f"Hello, {name}! You are {age}.")  # Hello, Alice! You are 30.

Formatting Options

Inside {}, you can use format specs just like str.format():

pi = 3.14159265
print(f"Pi rounded: {pi:.2f}")    # Pi rounded: 3.14
print(f"Binary: {age:b}")          # Binary: 11110
print(f"Padded: {age:0>4}")        # Padded: 0030

Expression and Debugging Support (Python 3.8+)

You can even put more complex stuff in there:

print(f"Next year I'll be {age + 1}.")  # Next year I'll be 31.

Plus, Python 3.8 added debugging support:

print(f"{name=}, {age=}")  # name='Alice', age=30

That {var=} shows both the name and value, super handy for quick prints.

Numeric Literal Underscores: Readable Numbers

Big numbers can be hard to parse at a glance. Python 3.6+ lets you sprinkle _ inside numeric literals:

# Integers:
one_million = 1_000_000
binary_mask = 0b_1111_0000
hex_color   = 0xFF_FF_FF

# Floats:
ratio = 3.14_15_92

The underscores don’t affect the value, they just help you read big numbers quickly.

A Taste of Extra Sugar

Here’s a small one: trailing commas in tuples, lists, and function arguments are totally fine, and sometimes encouraged for cleaner diffs:

points = [
    (0, 0),
    (1, 2),
    (2, 4),  # note trailing comma!
]
def foo(
    a,
    b,
    c,  # trailing comma here too
):
    pass

That way if you add a new line later, your diff only shows the new line.

That’s it for part five: f-strings, numeric literal underscores, and a pinch of extra sugar to keep your code neat. Next up, we’ll dig into dataclasses and context variables for super-simple data containers and async context management. Happy coding!