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The comparison operators, i.e. ==, !=, <, >, <=, >=, is, is not, in and not incite-ref-20[16] are used on all manner of values. Numbers, strings, sequences, and mappings can all be compared. In Python 3, disparate types (such as a str and an int) do not have a consistent relative ordering, and attempts to compare these types raises a TypeError exception. While it was possible to compare disparate types in Python 2 (for example, whether a string was greater-than or less-than an integer), the ordering was undefined; this was considered a historical design quirk and was ultimately removed in Python 3.

Chained comparison expressions such as a < b < c have roughly the meaning that they have in mathematics, rather than the unusual meaning found in C and similar languages. The terms are evaluated and compared in order. The operation has short-circuit semantics, meaning that evaluation is guaranteed to stop as soon as a verdict is clear: if a < b is false, c is never evaluated as the expression cannot possibly be true anymore.

For expressions without side effects, a < b < c is equivalent to a < b and b < c. However, there is a substantial difference when the expressions have side effects. a < f(x) < b will evaluate f(x) exactly once, whereas a < f(x) and f(x) < b will evaluate it twice if the value of a is less than f(x) and once otherwise.

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