How to compile a string of Python code into a module whose functions can be called?

Question

In Python, I have a string of some Python source code containing functions like:

mySrc = \'\'\'
def foo():
    print(\"foo\")

def bar():
    print(\"bar\")
\'\'         


        

Answer 1

In Python 2, you want the magical compiler package:

>>> import compiler
>>> mod = compiler.parseFile("doublelib.py")
>>> mod
Module('This is an example module.\n\nThis is the docstring.\n',
       Stmt([Function(None, 'double', ['x'], [], 0,
                      'Return twice the argument',
                      Stmt([Return(Mul((Name('x'), Const(2))))]))]))
>>> from compiler.ast import *
>>> Module('This is an example module.\n\nThis is the docstring.\n',
...    Stmt([Function(None, 'double', ['x'], [], 0,
...                   'Return twice the argument',
...                   Stmt([Return(Mul((Name('x'), Const(2))))]))]))
Module('This is an example module.\n\nThis is the docstring.\n',
       Stmt([Function(None, 'double', ['x'], [], 0,
                      'Return twice the argument',
                      Stmt([Return(Mul((Name('x'), Const(2))))]))]))
>>> mod.doc
'This is an example module.\n\nThis is the docstring.\n'
>>> for node in mod.node.nodes:
...     print node
...
Function(None, 'double', ['x'], [], 0, 'Return twice the argument',
         Stmt([Return(Mul((Name('x'), Const(2))))]))
>>> func = mod.node.nodes[0]
>>> func.code
Stmt([Return(Mul((Name('x'), Const(2))))])

And in Python 3, it's built right in.

Answer 2

You have to both compile and execute it:

myMod = compile(mySrc, '', 'exec')
exec(myMod)
foo()

You can pass dicts to exec to stop foo from “leaking” out. Combine it with a module object created using types.ModuleType:

from types import ModuleType
…
compiled = compile(mySrc, '', 'exec')
module = ModuleType("testmodule")
exec(compiled, module.__dict__)