Finding the source code for built-in Python functions

Question

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

Let s go straight to your question  Finding the source code for built-in Python functions  The source code is located at 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  lt name of function gt   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   quot sorted quot   1  1   amp seq           return NULL       newlist   PySequence List seq       if  newlist    NULL          return NULL       callable    PyObject GetAttrId newlist   amp PyId sort       if  callable    NULL            Py DECREF newlist           return NULL             assert nargs  gt   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

User · Answer

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

User · Answer

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

User · Answer

As mentioned by  Jim  the file organization is described here  Reproduced for ease of discovery      For Python modules  the typical layout is   Lib  lt module gt  py Modules   lt module gt  c  if there   s also a C accelerator module  Lib test test  lt module gt  py Doc library  lt module gt  rst       For extension-only modules  the typical layout is   Modules  lt module gt module c Lib test test  lt module gt  py Doc library  lt module gt  rst       For builtin types  the typical layout is   Objects  lt builtin gt object c Lib test test  lt builtin gt  py Doc library stdtypes rst       For builtin functions  the typical layout is   Python bltinmodule c Lib test test builtin py Doc library functions rst       Some exceptions   builtin type int is at Objects longobject c builtin type str is at Objects unicodeobject c builtin module sys is at Python sysmodule c builtin module marshal is at Python marshal c Windows-only module winreg is at PC winreg c

User · Answer

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      gt  gt  gt  import randint      gt  gt  gt  from inspect import getsource    gt  gt  gt  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    gt  gt  gt  help str  Help on class str in module   builtin     class str basestring      str object     - gt  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   lt    gt  x y          contains                x   contains   y   lt    gt  y in x          eq                x   eq   y   lt    gt  x  y          format                S   format   format spec  - gt  string            Return a formatted version of S as described by format spec           ge                x   ge   y   lt    gt  x gt  y          getattribute        -- More  --

[python] Finding the source code for built-in Python functions?

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