Python Join List with Underscore [The Most Pythonic Way]

The '_'.join(list) method on the underscore string '_' glues together all strings in the list using the underscore string as a delimiter—and returns a new string. For example, the expression '_'.join(['a', 'b', 'c']) returns the new string 'a_b_c'.

Definition and Usage

The string.join(iterable) method joins the string elements in the iterable to a new string by using the string on which it is called as a delimiter.

Here’s a short example:

friends = ['Alice', 'Bob', 'Carl']

# Empty delimiter string ''
print(''.join(friends))
# AliceBobCarl

# Delimiter string '_'
print('_'.join(friends))
# Alice_Bob_Carl

The string elements in the list friends are concatenated using the delimiter string '' in the first example and the underscore character '_' in the second example.

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Syntax

You can call this method on each list object in Python. Here’s the syntax:

string.join(iterable)

ArgumentDescription
iterableThe elements to be concatenated.

Code Puzzle

To practice what you’ve learned so far, feel free to solve the following interactive code puzzle:

Exercise: Guess the output and check if you were right by running the interactive code shell.

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