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<title>5.10 Boolean operations
</title>
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<H1><A NAME=
"SECTION0071000000000000000000"></A><A NAME=
"Booleans"></A>
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Boolean operations have the lowest priority of all Python operations:
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<td><a class='grammartoken'
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<a class='grammartoken'
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<td><a id='tok-or_test' xml:id='tok-or_test'
>or_test
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<td><a class='grammartoken'
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<a class='grammartoken'
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<td><a id='tok-and_test' xml:id='tok-and_test'
>and_test
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<td><a class='grammartoken'
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</a> |
<a class='grammartoken'
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href=
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<td><a id='tok-not_test' xml:id='tok-not_test'
>not_test
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<td><a class='grammartoken'
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"not" <a class='grammartoken'
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In the context of Boolean operations, and also when expressions are
used by control flow statements, the following values are interpreted
as false:
<code>False
</code>,
<code>None
</code>, numeric zero of all types, and empty
strings and containers (including strings, tuples, lists, dictionaries,
sets and frozensets). All other values are interpreted as true.
The operator
<tt class=
"keyword">not
</tt> yields
<code>True
</code> if its argument is false,
<code>False
</code> otherwise.
<a id='l2h-
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The expression
<code><var>x
</var> and
<var>y
</var></code> first evaluates
<var>x
</var>; if
<var>x
</var> is false, its value is returned; otherwise,
<var>y
</var> is
evaluated and the resulting value is returned.
<a id='l2h-
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></a>
The expression
<code><var>x
</var> or
<var>y
</var></code> first evaluates
<var>x
</var>; if
<var>x
</var> is true, its value is returned; otherwise,
<var>y
</var> is
evaluated and the resulting value is returned.
<a id='l2h-
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></a>
(Note that neither
<tt class=
"keyword">and
</tt> nor
<tt class=
"keyword">or
</tt> restrict the value
and type they return to
<code>False
</code> and
<code>True
</code>, but rather return the
This is sometimes useful, e.g., if
<code>s
</code> is a string that should be
replaced by a default value if it is empty, the expression
<code>s or 'foo'
</code> yields the desired value. Because
<tt class=
"keyword">not
</tt> has to
invent a value anyway, it does not bother to return a value of the
same type as its argument, so e.g.,
<code>not 'foo'
</code> yields
<code>False
</code>,
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<span class=
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2.4.2, documentation updated on
28 September
2005.
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