Why does inspect() think map isn't built in?

Question

The following code returns false

import inspect print(inspect.isbuiltin(map)) 

But the map function is listed under "built-in" functions.

Why is it so?

Answer 1

The inspect.isbuiltin will only

Return true if the object is a built-in function or method.

The map builtin is a class, not a function or method:

>>> map <class 'map'> 

In fact, most "built-in functions" that return iterators are implemented as classes; calling them returns optimised instances instead of re-using some generic iterator class.

>>> zip  # zip iterator "function" is also a class <class 'zip'> >>> map(str, (1, 2, 34))  # map builds instances of map <map object at 0x103fa34f0> 

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In addition, keep in mind that the term "built-in" has two meanings in Python:

• A compiled object, i.e. built into the interpreter.
• A member of the builtins module, available in every module.

While most builtins are compiled for speed, this is no necessity.

If you want to check whether a name is part of builtins, do so via the module:

>>> import builtins >>> hasattr(builtins, "map") True >>> hasattr(builtins, "sum") True >>> hasattr(builtins, "reduce") False