Скачать или смотреть How to List an Array of Strings into Multiple Vertical Columns in Python

Learn how to format a list of strings into multiple columns ordered vertically using Python slicing and itertools for clean, readable output.
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This video is based on the question https://stackoverflow.com/q/79368560/ asked by the user 'Ecylin' ( https://stackoverflow.com/u/12100167/ ) and on the answer https://stackoverflow.com/a/79372300/ provided by the user 'Xerus Lord' ( https://stackoverflow.com/u/9955476/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

When printing a list of strings in multiple columns, the default approach usually orders them horizontally by rows:

[[See Video to Reveal this Text or Code Snippet]]

However, you might want to display them vertically in columns like this:

[[See Video to Reveal this Text or Code Snippet]]

This post explains how to transform a list into this vertical column format efficiently and neatly.



The Problem

Given a list (e.g., ['A','B','C','D','E','F','G','H']) and a column count, how can you print the values so they fill columns from top to bottom, then move right?

Current horizontal approach:

[[See Video to Reveal this Text or Code Snippet]]

This prints by rows, but we want vertical ordering.



The Core Concept: Python Slicing with Steps

Python slicing supports a third parameter as the step, letting you extract every n-th element:

[[See Video to Reveal this Text or Code Snippet]]

This step slicing is the key to vertical printing: each column corresponds to elements sampled at fixed step intervals starting at different offsets.



Efficient Solution Using Itertools' islice

For large datasets, using iterators saves memory. itertools.islice lets you slice iterators without generating full lists.

Example:

[[See Video to Reveal this Text or Code Snippet]]

Output:

[[See Video to Reveal this Text or Code Snippet]]



Adding Column Width Formatting for Readability

To print aligned columns, calculate the maximum width per column and pad strings accordingly.

Using Python 3.10's itertools.batched for grouping and f-strings for padding:

[[See Video to Reveal this Text or Code Snippet]]

Output:

[[See Video to Reveal this Text or Code Snippet]]

(Note: trailing spaces appear when columns are uneven.)



Alternative Approach Using zip_longest

A cleaner variant inspired by ChatGPT uses zip_longest to rearrange the list:

[[See Video to Reveal this Text or Code Snippet]]

Output:

[[See Video to Reveal this Text or Code Snippet]]



Summary

Use slice with steps (list[::n]) to extract vertical columns.

Use itertools.islice for memory-efficient iteration.

Calculate max column widths to align output.

itertools.batched and zip_longest simplify grouping and printing.

This approach dynamically works for any list size and column count, producing clean, vertically ordered columns.