Скачать или смотреть How to Convert a String of Digits to a List of Bytes in Python Correctly

Learn an effective way to convert a string of decimal digits into a list of byte-sized integers (0-255) in Python, preserving every digit and maximizing chunk size.
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This video is based on the question https://stackoverflow.com/q/79511907/ asked by the user 'Ξένη Γήινος' ( https://stackoverflow.com/u/16383578/ ) and on the answer https://stackoverflow.com/a/79512408/ provided by the user 'SIGHUP' ( https://stackoverflow.com/u/17580381/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

When processing a string made of decimal digits, you might want to break it into chunks that represent valid byte values (0-255). The tricky part is to segment the digits into the longest possible numbers without exceeding 255, while preserving every digit exactly.

For example, given the string:

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

You want to get:

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And for strings of zeros like:

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You want each zero preserved as a byte:

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

Additionally, reconstructing the original string by concatenating the bytes as strings should yield the original input:

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



The Challenge

A naive approach might try to convert digits greedily, but errors arise especially with leading zeros or when switching from one chunk to the next. The common pitfalls are:

Losing zeros at the beginning or between chunks.

Incorrect chunking that doesn't guarantee the longest valid sequences.

Off-by-one errors when appending the last chunk.



A Correct, Concise Solution

The Python function below solves the problem cleanly:

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



Explanation

We first convert all leading zeros into separate zero bytes to prevent losing them.

For the remaining string, we try to form the longest valid number (<= 255) by appending digits.

If adding a digit exceeds 255, we append the current chunk and start a new one.

Isolated zeros (including multiple zeros in a row) are handled to ensure none get lost.



Examples & Output

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

Output:

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Each output respects the condition that joining their string forms returns the original input.



Conclusion

This approach provides a reliable, straightforward method to convert digit strings into byte lists while preserving every digit and favoring the longest sequences under 256. It handles special cases like multiple zeros naturally without complicated regex or lookahead logic.