PythonCharmers/python-future

newbytes is unable to handle a generator as a parameter

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#288 opened on Jun 21, 2017

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0.20bughelp wanted

Description

After only checking that the parameter is Iterable, newbytes then checks the parameters len(). https://github.com/PythonCharmers/python-future/blob/39a066ed8c29a0b3a32adac2ffd407119fe9ea6d/src/future/types/newbytes.py#L106

https://repl.it/IwSF/2

print(repr(bytes.newbytes(x for x in range(0))))

Traceback (most recent call last):
  File "main.py", line 4, in <module>
    print(repr(bytes.newbytes(x for x in range(0))))
  File "/home/runner/bytes.py", line 103, in __new__
    if len(args[0]) == 0:
TypeError: object of type 'generator' has no len()

Including a check for Sized as well avoids this.

if isinstance(args[0], Sized) and len(args[0]) == 0:

https://repl.it/IwSF/1

Contributor guide

Tech stack
python
Domain
backend
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
under 1 hour
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Python basicsUnderstanding of iterables
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
85
Research direction
The bug is in `newbytes. new ` in `src/future/types/newbytes.py` around line 106. The code currently checks `len(args[0])` without confirming the argument supports `len()`. Generators are iterable but not sized, causing a `TypeError`. The fix is to add an `isinstance(args[0], Sized)` check before calling `len()`. You'll need to import `Sized` from `collections.abc` (or `collections` depending on Python version). Review the existing imports and modify the condition accordingly.