Think Python - Chapter 03 - Functions

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3.1 Function calls In the context of programming, a function is a named sequence of statements that performs a computation. When you define a function, you specify the name and the sequence of statements. Later, you can “call” the function by name. We have already seen one example of a function call:
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 <pre class="blockcode">>>> type(32)
<type 'int'></pre>
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The name of the function is type. The expression in parentheses is called the argument of the function. The result, for this function, is the type of the argument. It is common to say that a function “takes” an argument and “returns” a result. The result is called the return value.
3.2 Type conversion functions Python provides built-in functions that convert values from one type to another. The int function takes any value and converts it to an integer, if it can, or complains otherwise:
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 <pre class="blockcode">>>> int('32')
32
>>> int('Hello')
ValueError: invalid literal for int(): Hello</pre>
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int can convert floating-point values to integers, but it doesn’t round off; it chops off the fraction part:
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 <pre class="blockcode">>>> int(3.99999)
3
>>> int(-2.3)
-2</pre>
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float converts integers and strings to floating-point numbers:
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 <pre class="blockcode">>>> float(32)
32.0
>>> float('3.14159')
3.14159</pre>
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Finally, str converts its argument to a string:
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 <pre class="blockcode">>>> str(32)
'32'
>>> str(3.14159)
'3.14159'</pre>
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3.3 Math functions Python has a math module that provides most of the familiar mathematical functions. A module is a file that contains a collection of related functions. Before we can use the module, we have to import it:
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 <pre class="blockcode">>>> import math</pre>
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This statement creates a module object named math. If you print the module object, you get some information about it:
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 <pre class="blockcode">>>> print math
<module '<span style="color:#800000