Finding the source code for built-in Python functions?
PythonPython InternalsPython Problem Overview
Is there a way to see how built in functions work in python? I don't mean just how to use them, but also how were they built, what is the code behind sorted or enumerate etc...?
Python Solutions
Solution 1 - Python
Since Python is open source you can read the source code.
To find out what file a particular module or function is implemented in you can usually print the __file__ attribute. Alternatively, you may use the inspect module, see the section Retrieving Source Code in the documentation of inspect.
For built-in classes and methods this is not so straightforward since inspect.getfile and inspect.getsource will return a type error stating that the object is built-in. However, many of the built-in types can be found in the Objects sub-directory of the Python source trunk. For example, see here for the implementation of the enumerate class or here for the implementation of the list type.
Solution 2 - Python
Here is a cookbook answer to supplement @Chris' answer, CPython has moved to GitHub and the Mercurial repository will no longer be updated:
-
Install Git if necessary.
-
git clone https://github.com/python/cpython.git -
Code will checkout to a subdirectory called
cpython->cd cpython -
Let's say we are looking for the definition of
print()... -
egrep --color=always -R 'print' | less -R -
Aha! See
Python/bltinmodule.c->builtin_print()
Enjoy.
Solution 3 - Python
I had to dig a little to find the source of the following Built-in Functions as the search would yield thousands of results. (Good luck searching for any of those to find where it's source is)
Anyway, all those functions are defined in bltinmodule.c Functions start with builtin_{functionname}
>Built-in Source: https://github.com/python/cpython/blob/master/Python/bltinmodule.c > >For Built-in Types: https://github.com/python/cpython/tree/master/Objects
Solution 4 - Python
The iPython shell makes this easy: function? will give you the documentation. function?? shows also the code. BUT this only works for pure python functions.
Then you can always download the source code for the (c)Python.
If you're interested in pythonic implementations of core functionality have a look at PyPy source.
Solution 5 - Python
2 methods,
- You can check usage about snippet using
help() - you can check hidden code for those modules using
inspect
1) inspect:
use inpsect module to explore code you want... NOTE: you can able to explore code only for modules (aka) packages you have imported
for eg:
>>> import randint
>>> from inspect import getsource
>>> getsource(randint) # here i am going to explore code for package called `randint`
2) help():
you can simply use help() command to get help about builtin functions as well its code.
for eg:
if you want to see the code for str() , simply type - help(str)
it will return like this,
>>> help(str)
Help on class str in module __builtin__:
class str(basestring)
| str(object='') -> string
|
| Return a nice string representation of the object.
| If the argument is a string, the return value is the same object.
|
| Method resolution order:
| str
| basestring
| object
|
| Methods defined here:
|
| __add__(...)
| x.__add__(y) <==> x+y
|
| __contains__(...)
| x.__contains__(y) <==> y in x
|
| __eq__(...)
| x.__eq__(y) <==> x==y
|
| __format__(...)
| S.__format__(format_spec) -> string
|
| Return a formatted version of S as described by format_spec.
|
| __ge__(...)
| x.__ge__(y) <==> x>=y
|
| __getattribute__(...)
-- More --
Solution 6 - Python
Quite an unknown resource is the Python Developer Guide.
In a (somewhat) recent GH issue, a new chapter was added for to address the question you're asking: CPython Source Code Layout. If something should change, that resource will also get updated.
Solution 7 - Python
Let's go straight to your question.
Finding the source code for built-in Python functions?
The source code is located at cpython/Python/bltinmodule.c
To find the source code in the GitHub repository go here. You can see that all in-built functions start with builtin_<name_of_function>, for instance, sorted() is implemented in builtin_sorted.
For your pleasure I'll post the implementation of sorted():
builtin_sorted(PyObject *self, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
{
PyObject *newlist, *v, *seq, *callable;
/* Keyword arguments are passed through list.sort() which will check
them. */
if (!_PyArg_UnpackStack(args, nargs, "sorted", 1, 1, &seq))
return NULL;
newlist = PySequence_List(seq);
if (newlist == NULL)
return NULL;
callable = _PyObject_GetAttrId(newlist, &PyId_sort);
if (callable == NULL) {
Py_DECREF(newlist);
return NULL;
}
assert(nargs >= 1);
v = _PyObject_FastCallKeywords(callable, args + 1, nargs - 1, kwnames);
Py_DECREF(callable);
if (v == NULL) {
Py_DECREF(newlist);
return NULL;
}
Py_DECREF(v);
return newlist;
}
As you may have noticed, that's not Python code, but C code.
Solution 8 - Python
As mentioned by @Jim, the file organization is described here. Reproduced for ease of discovery:
> For Python modules, the typical layout is:
>
> Lib/