Function Mangling

This module provides utilities for extracting information about python functions.

AUTHORS:

  • Tom Boothby (2009): Original version in Python
  • Simon King (2011): Use Cython. Speedup of fix_to_pos, cleaning documentation.
class sage.misc.function_mangling.ArgumentFixer

Bases: object

This class provides functionality to normalize the arguments passed into a function. While the various ways of calling a function are perfectly equivalent from the perspective of the callee, they don’t always look the same for an object watching the caller. For example,

sage: def f(x = 10):
....:     return min(1,x)

the following calls are equivalent,

sage: f()
1
sage: f(10)
1
sage: f(x=10)
1

but from the perspective of a wrapper, they are different:

sage: def wrap(g):
....:     def _g(*args,**kwargs):
....:         print("{} {}".format(args, kwargs))
....:         return g(*args, **kwargs)
....:     return _g
sage: h = wrap(f)
sage: t = h()
() {}
sage: t = h(10)
(10,) {}
sage: t = h(x=10)
() {'x': 10}

For the purpose of cached functions, it is important not to distinguish between these uses.

INPUT:

  • f – a function
  • classmethod – boolean (default False) – True if the function is a classmethod and therefore the first argument is expected to be the class instance. In that case, we ignore the first argument.

EXAMPLES:

sage: from sage.misc.function_mangling import ArgumentFixer
sage: def wrap2(g):
....:     af = ArgumentFixer(g)
....:     def _g(*args, **kwargs):
....:         print(af.fix_to_pos())
....:         return g(*args,**kwargs)
....:     return _g
sage: h2 = wrap2(f)
sage: t = h2()
((10,), ())
sage: t = h2(10)
((10,), ())
sage: t = h2(x=10)
((10,), ())
sage: class one:
....:    def __init__(self, x = 1):
....:       self.x = x
sage: af = ArgumentFixer(one.__init__, classmethod=True)
sage: af.fix_to_pos(1,2,3,a=31,b=2,n=3)
((1, 2, 3), (('a', 31), ('b', 2), ('n', 3)))
f
fix_to_named(*args, **kwargs)

Normalize the arguments with a preference for named arguments.

INPUT:

  • any positional and named arguments.

OUTPUT:

We return a tuple

\((e_1, e_2, ..., e_k), ((n_1, v_1), ... , (n_m, v_m))\)

where \(n_1, ... , n_m\) are the names of the arguments and \(v_1, ..., v_m\) are the values passed in; and \(e_1, ..., e_k\) are the unnamed arguments. We minimize \(k\).

The defaults are extracted from the function and filled into the list K of named arguments. The names \(n_1, ..., n_t\) are in order of the function definition, where \(t\) is the number of named arguments. The remaining names, \(n_{t+1}, ..., n_m\) are given in alphabetical order. This is useful to extract the names of arguments, but does not maintain equivalence of

A,K = self.fix_to_pos(...)
self.f(*A,**dict(K))`

and

self.f(...)

in all cases.

EXAMPLES:

sage: from sage.misc.function_mangling import ArgumentFixer
sage: def sum3(a,b,c=3,*args,**kwargs):
....:     return a+b+c
sage: AF = ArgumentFixer(sum3)
sage: AF.fix_to_named(1,2,3,4,5,6,f=14,e=16)
((4, 5, 6), (('a', 1), ('b', 2), ('c', 3), ('e', 16), ('f', 14)))
sage: AF.fix_to_named(1,2,f=14)
((), (('a', 1), ('b', 2), ('c', 3), ('f', 14)))
fix_to_pos(*args, **kwds)

Normalize the arguments with a preference for positional arguments.

INPUT:

Any positional or named arguments

OUTPUT:

We return a tuple

\((e_1, e_2, ..., e_k), ((n_1, v_1), ... , (n_m, v_m))\)

where \(n_1, ... , n_m\) are the names of the arguments and \(v_1, ..., v_m\) are the values passed in; and \(e_1, ..., e_k\) are the unnamed arguments. We minimize \(m\).

The commands

A,K = self.fix_to_pos(...)
self.f(*A,**dict(K))

are equivalent to

self.f(...)

though defaults are extracted from the function and appended to the tuple A of positional arguments. The names \(n_1, ..., n_m\) are given in alphabetical order.

EXAMPLES:

sage: from sage.misc.function_mangling import ArgumentFixer
sage: def do_something(a, b, c=3, *args, **kwargs):
....:     print("{} {} {} {} {}".format(a, b, c, args,
....:                                   sorted(kwargs.items())))
sage: AF = ArgumentFixer(do_something)
sage: A, K = AF.fix_to_pos(1, 2, 3, 4, 5, 6, f=14, e=16)
sage: print("{} {}".format(A, K))
(1, 2, 3, 4, 5, 6) (('e', 16), ('f', 14))
sage: do_something(*A, **dict(K))
1 2 3 (4, 5, 6) [('e', 16), ('f', 14)]
sage: do_something(1, 2, 3, 4, 5, 6, f=14, e=16)
1 2 3 (4, 5, 6) [('e', 16), ('f', 14)]