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