Compare string to float in Python

Question

I tried this in python shell

>>> a='apple'
>>> b=11.1
>>> a>b
True
>>> a
'apple'
>>> b>a
False

Can someone explain to me how a>b is True? When a is an string and b is float.

http://stackoverflow.com/questions/3270680/how-does-python-compare-string-and-int/3270689#3270689 — Joran Beasley, Oct 31 '13 at 17:58
You can find more info here http://stackoverflow.com/questions/3270680/how-does-python-compare-string-and-int — jramirez, Oct 31 '13 at 17:58
@jramirez I don't know if you have enough rep points but the most helpful thing is to flag this as a duplicate. — Joe, Oct 31 '13 at 17:59

6502 · Accepted Answer · 2013-10-31T18:18:32.703

5

Order comparison between elements of different types was a "design bug" in Python 2.x that has been removed in Python 3 (where you get a runtime error).

Correcting it wasn't an option before 3.x because of a lot of existing software that does sorting on heterogeneous containers (and version 3 is the first in which backward compatibility is intentionally broken).

In Python 2.x you can compare anything for </>, with the only exception of complex numbers where this is explicitly forbidden.

The ordering result of comparison of different types is arbitrary but fixed at least for a given run of the Python interpreter, see http://docs.python.org/2/reference/expressions.html#not-in . Values of different non-numeric types are always considered different.

edited Oct 31 '13 at 18:18

answered Oct 31 '13 at 17:59

6502

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Putting it in simple terms It is bug in 2.x, gives quite random results and removed from 3.x – Gaurav Agarwal Oct 31 '13 at 18:08
1

@GauravAgarwal: "random" is excessive, it's arbitrary (e.g. if `'a'<3` then any string is less than any integer) and you can for example implement a sorting because you get transitivity. It was a design bug that could not be fixed before python 3.x because people started depending on it. – 6502 Oct 31 '13 at 18:12

score 1 · Answer 2 · answered Oct 31 '13 at 18:01

In Python 2, comparison between incomparable types often "works", giving meaningless results. Sometimes it's fun: 'aleph0' > float('+inf'). But most of the time it's just silly.

So Python 3 has removed this, and 'a' > 1.0 quite reasonably raises a TypeError under it.

Compare string to float in Python

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