Unlock Python’s Secret: Master the Underscore (_) for Cleaner Code

The underscore '_' is a gem in Python, offering many handy uses that often go unnoticed; this article explains the various ways to employ a single underscore in Python code and the scenarios where it shines.

1. Discarding Variables

When a variable is unnecessary, instead of creating a named placeholder like temp or temporary_variable, you can use '_' to indicate the value should be ignored.

first_name, middle_name, last_name = ["fname", "mname", "lname"]
print(first_name, last_name)

Since middle_name is not needed, replace it with '_' to mark it as a discarded variable:

first_name, _, last_name = ["fname", "mname", "lname"]
print(first_name, last_name)

This does not affect interpreter behavior; it simply signals to developers that the variable is irrelevant.

2. Unused Loop Variables

In loops where the iterator value is not required, you can replace the loop variable with '_' to clarify its irrelevance.

for x in range(10):
    num = num * 10

Here, x is unused. Using '_' makes the intent clear:

for _ in range(10):
    num = num * 10

You can also apply this pattern with enumerate when you only need the index:

word_list = ["word-1", "word-2", "word-3", "word-4"]
for idx, _ in enumerate(word_list):
    print(idx)

3. Making Large Numbers More Readable

Python allows underscores inside numeric literals to improve readability, similar to digit grouping in formatted numbers.

num_1 = 134578920
num_2 = 134_578_920
print(num_1)
print(num_2)

Using f-strings, you can format the output with commas or underscores:

print(f"{num_1:,}")
print(f"{num_1:_}")

4. REPL Tricks

In an interactive REPL session, '_' automatically stores the result of the last expression, allowing quick reuse without defining a new variable.

>> 2 + 3
5
>>> _
5

This shortcut speeds up exploratory coding.

5. Legal Variable Name

Technically, '_' is a valid identifier and can be used as a regular variable name, but it is strongly discouraged unless you intend to prank others.

_ = "Never Gonna Give You Up"
print(_)