Why is '362' > 378?

Question

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How does Python compare string and int?

An intern was just asking me to help debug code that looked something like this:

widths = [image.width for image in images]
widths.append(374)
width = max(widths)

...when the first line should have been:

widths = [int(image.width) for image in images]

Thus, the code was choosing the string '364' rather than the integer 374. How on earth does python compare a string and an integer? I could understand comparing a single character (if python had a char datatype) to an integer, but I don't see any straightforward way to compare a string of characters to an integer.

Answer 1

Python 2.x compares every built-in type to every other. From the docs:

Objects of different types, except different numeric types and different string types, never compare equal; such objects are ordered consistently but arbitrarily (so that sorting a heterogeneous array yields a consistent result).

This "arbitrary order" in CPython is actually sorted by type name.

In Python 3.x, you will get a TypeError if you try to compare a string to an integer.

Answer 2

When comparing values of incompatible types in python 2.x, the ordering will be arbitrary but consistent. This is to allow you to put values of different types in a sorted collection.

In CPython 2.x any string will always be higher than any integer, but as I said that's arbitrary. The actual ordering does not matter, it is just important that the ordering is consistent (i.e. you won't get a case where e.g. x > y and y > z, but z > x).

Answer 3

From the documentation:

Most other objects of built-in types compare unequal unless they are the same object; the choice whether one object is considered smaller or larger than another one is made arbitrarily but consistently within one execution of a program

Hope this is clear enough - like it has been said, it is arbitrary.