NameError even with a direct, unconditional assignment on the line above

Question

Just explain me how it is possible:

сhar = input()
print(char)

Traceback (most recent call last): File "test.py", line 2, in print(char) NameError: name 'char' is not defined

To make things more interesting, consider running that code in repl.it with double-checked python version:

import sys
print(f'Python version on this machine:\n{sys.version}')
сhar = input()
print(char)

Python version on this machine:
3.7.4 (default, Jul 13 2019, 14:20:24)
[GCC 6.3.0 20170516]
type anything
Traceback (most recent call last):
File "main.py", line 5, in
print(char)
NameError: name 'char' is not defined

How is this in any way behavior *of `input()`*? `input()` has nothing to do with how its returned value is bound to a name. — Charles Duffy, Jul 31 '19 at 19:49
Are you sure your `char = input()` is not commented out and you are running the whole thing? — FatihAkici, Jul 31 '19 at 19:50
@Tomerikoo. I can reporduce this by, e.g., pasting the two lines into IPython as a unit. — Mad Physicist, Jul 31 '19 at 19:51
I can replicate it, but only copying-and-pasting from the question. Name the destination variable to, say, `result` and it no longer happens. — Charles Duffy, Jul 31 '19 at 19:52
And this folks, is why it is important to create an example that people can copy and paste into a terminal. — Mad Physicist, Jul 31 '19 at 19:55
Related: [Python the same char not equals](https://stackoverflow.com/q/36137602/674039) — wim, Jul 31 '19 at 21:22

wim · Accepted Answer · 2019-07-31T19:55:41.277

11

Unicode identifier names.

>>> "char" == "сhar" 
False

One of those c is a vanilla 'LATIN SMALL LETTER C' but the other is chr(0x441), i.e. 'CYRILLIC SMALL LETTER ES'. On a typical machine they will render to the terminal with very similar looking (or exactly same) glyphs.

edited Jul 31 '19 at 19:55

answered Jul 31 '19 at 19:50

wim

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1

Could you elaborate please? – Mad Physicist Jul 31 '19 at 19:51
2

@StardustGogeta Are you typing it in, or are you copy-pasting? – iz_ Jul 31 '19 at 19:52
1

I believe you have to copy paste it. @StardustGogeta – Axiumin_ Jul 31 '19 at 19:52
@iz_ Good catch, I never would have thought about that. – StardustGogeta Jul 31 '19 at 19:53
5

@wim How were you able to identify the issue so fast? Are you using a font that does not have identical glyphs, or had you seen this before? – Mad Physicist Jul 31 '19 at 19:54
4

I have seen similar underhanded tricks before. In chrome browser, you can ctrl+f and type c you will notice one c from the question doesn't "highlight" on the page. – wim Jul 31 '19 at 19:56
@MadPhysicist Try this: `list(ord(c) for c in 'сhar')` – Roland Smith Jul 31 '19 at 19:57
@RolandSmith. I obviously did. My question was how wim immediately knew to do that. Of course it's the most plausible solution in hindsight... – Mad Physicist Jul 31 '19 at 19:58
@MadPhysicist As for me, I identified it by copying it to pycharm. It tells you `Identifier contains symbols from different languages: [LATIN, CYRILLIC] ...` – Mark G Jul 31 '19 at 20:09

Mark G · Answer 2 · 2019-07-31T19:58:24.300

7

Your char = input() contains the cyrillic character с (see here) Whereas the print(char) is purely latin.

This also reminds me of the greek question mark prank, where the characters for semicolon and the question mark are rendered almost the same: ;;

Edit: wim was faster

edited Jul 31 '19 at 19:58

answered Jul 31 '19 at 19:52

Mark G

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greek question mark is in my opinion much more brutal – theuses Jul 31 '19 at 19:58

NameError even with a direct, unconditional assignment on the line above

2 Answers2