Modules, Classes, and Methods

In , you saw that a module is a kind of object, one that can contain functions and other variables. There is another kind of object that is similar to a module: a class. You’ve been using classes all along, probably without realizing it: a class is how Python represents a type.

You may have called built-in function help on int, float, bool, or str. Let’s do that now with str (note that the first line indicates it’s a class):

​	​>>>​​ ​​help(str)​
​	Help on class str in module builtins:
​
​	class str(object)
​	| str(object='') -> str
​	| str(bytes_or_buffer[, encoding[, errors]]) -> str
​	|
​	| Create a new string object from the given object. If encoding or
​	| errors is specified, then the object must expose a data buffer
​	| that will be decoded using the given encoding and error handler.
​	| Otherwise, returns the result of object.__str__() (if defined)
​	| or repr(object).
​	| encoding defaults to 'utf-8'.
​	| errors defaults to 'strict'.
​	|
​	| Methods defined here:
​	|
​	| __add__(self, value, /)
​	| Return self+value.
​	|
​	| __contains__(self, key, /)
​	| Return bool(key in self).
​
​	[Lots of other names with leading and trailing underscores not shown here.]
​
​	| capitalize(self, /)
​	| Return a capitalized version of the string.
​	|
​	| More specifically, make the first character have upper case and the
​	| rest lower case.
​	|
​	| casefold(self, /)
​	| Return a version of the string suitable for caseless comparisons.
​	|
​	| center(self, width, fillchar=' ', /)
​	| Return a centered string of length width.
​	|
​	| Padding is done using the specified fill character (default is a
​	| space).
​	|
​	| count(self, sub[, start[, end]], /)
​	| Return the number of non-overlapping occurrences of substring sub
​	| in string S[start:end].
​
​	[There are many more of these as well.]

Near the top of this documentation is the description of the str function:

​	| str(bytes_or_buffer[, encoding[, errors]]) -> str
​	|
​	| Create a new string object from the given object.

It explains how to use str as a function: you can call it to create a string. For example, str(17) creates the string ’17’.

Functions that create new objects are called constructors. Function str is a constructor for strings. Functions int, float, and bool are constructors for the namesake data types. You will learn more about constructors in Chapter 14, .

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