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Boolean expressions

19 一月, 2016 - 11:46

A boolean expression is an expression that is either true or false. The following examples use the operator ==, which compares two operands and produces True if they are equal and False otherwise:

>>> 5 == 5
True
>>> 5 == 6
False

True and False are special values that belong to the type bool; they are not strings:

>>> type(True)
<type 'bool'>
>>> type(False)
<type 'bool'>

The == perator is one of the comparison operators; the others are:

Table 3.1 Comparison operators
x != y # x is not equal to y
x > y    # x is greater than y
x < y # x is less than y
x >= y # x is greater than or equal to y
x <= y # x is less than or equal to y
x is y # x is the same as y
x is not y # x is not the same as y

Although these operations are probably familiar to you, the Python symbols are different from the mathematical symbols. A common error is to use a single equal sign (=) instead of a double equal sign (==). Remember that = is an assignment operator and == is a comparison operator. There is no such thing as =< or =>.