add inspect.getcallargs, which binds function arguments like a normal call #3135

Patch by George Sakkis

Doc/library/inspect.rst

@@ -504,6 +504,32 @@ Classes and functions
    metatype is in use, cls will be the first element of the tuple.
 
 
+.. function:: getcallargs(func[, *args][, **kwds])
+
+   Bind the *args* and *kwds* to the argument names of the Python function or
+   method *func*, as if it was called with them. For bound methods, bind also the
+   first argument (typically named ``self``) to the associated instance. A dict
+   is returned, mapping the argument names (including the names of the ``*`` and
+   ``**`` arguments, if any) to their values from *args* and *kwds*. In case of
+   invoking *func* incorrectly, i.e. whenever ``func(*args, **kwds)`` would raise
+   an exception because of incompatible signature, an exception of the same type
+   and the same or similar message is raised. For example::
+
+    >>> from inspect import getcallargs
+    >>> def f(a, b=1, *pos, **named):
+    ...     pass
+    >>> getcallargs(f, 1, 2, 3)
+    {'a': 1, 'named': {}, 'b': 2, 'pos': (3,)}
+    >>> getcallargs(f, a=2, x=4)
+    {'a': 2, 'named': {'x': 4}, 'b': 1, 'pos': ()}
+    >>> getcallargs(f)
+    Traceback (most recent call last):
+    ...
+    TypeError: f() takes at least 1 argument (0 given)
+
+   .. versionadded:: 2.7
+
+
 .. _inspect-stack:
 
 The interpreter stack

Lib/inspect.py

@@ -17,7 +17,7 @@ Here are some of the useful functions provided by this module:
     getmodule() - determine the module that an object came from
     getclasstree() - arrange classes so as to represent their hierarchy
 
-    getargspec(), getargvalues() - get info about function arguments
+    getargspec(), getargvalues(), getcallargs() - get info about function arguments
     formatargspec(), formatargvalues() - format an argument spec
     getouterframes(), getinnerframes() - get info about frames
     currentframe() - get the current stack frame
@@ -884,6 +884,89 @@ def formatargvalues(args, varargs, varkw, locals,
         specs.append(formatvarkw(varkw) + formatvalue(locals[varkw]))
     return '(' + string.join(specs, ', ') + ')'
 
+def getcallargs(func, *positional, **named):
+    """Get the mapping of arguments to values.
+
+    A dict is returned, with keys the function argument names (including the
+    names of the * and ** arguments, if any), and values the respective bound
+    values from 'positional' and 'named'."""
+    args, varargs, varkw, defaults = getargspec(func)
+    f_name = func.__name__
+    arg2value = {}
+
+    # The following closures are basically because of tuple parameter unpacking.
+    assigned_tuple_params = []
+    def assign(arg, value):
+        if isinstance(arg, str):
+            arg2value[arg] = value
+        else:
+            assigned_tuple_params.append(arg)
+            value = iter(value)
+            for i, subarg in enumerate(arg):
+                try:
+                    subvalue = next(value)
+                except StopIteration:
+                    raise ValueError('need more than %d %s to unpack' %
+                                     (i, 'values' if i > 1 else 'value'))
+                assign(subarg,subvalue)
+            try:
+                next(value)
+            except StopIteration:
+                pass
+            else:
+                raise ValueError('too many values to unpack')
+    def is_assigned(arg):
+        if isinstance(arg,str):
+            return arg in arg2value
+        return arg in assigned_tuple_params
+    if ismethod(func) and func.im_self is not None:
+        # implicit 'self' (or 'cls' for classmethods) argument
+        positional = (func.im_self,) + positional
+    num_pos = len(positional)
+    num_total = num_pos + len(named)
+    num_args = len(args)
+    num_defaults = len(defaults) if defaults else 0
+    for arg, value in zip(args, positional):
+        assign(arg, value)
+    if varargs:
+        if num_pos > num_args:
+            assign(varargs, positional[-(num_pos-num_args):])
+        else:
+            assign(varargs, ())
+    elif 0 < num_args < num_pos:
+        raise TypeError('%s() takes %s %d %s (%d given)' % (
+            f_name, 'at most' if defaults else 'exactly', num_args,
+            'arguments' if num_args > 1 else 'argument', num_total))
+    elif num_args == 0 and num_total:
+        raise TypeError('%s() takes no arguments (%d given)' %
+                        (f_name, num_total))
+    for arg in args:
+        if isinstance(arg, str) and arg in named:
+            if is_assigned(arg):
+                raise TypeError("%s() got multiple values for keyword "
+                                "argument '%s'" % (f_name, arg))
+            else:
+                assign(arg, named.pop(arg))
+    if defaults:    # fill in any missing values with the defaults
+        for arg, value in zip(args[-num_defaults:], defaults):
+            if not is_assigned(arg):
+                assign(arg, value)
+    if varkw:
+        assign(varkw, named)
+    elif named:
+        unexpected = next(iter(named))
+        if isinstance(unexpected, unicode):
+            unexpected = unexpected.encode(sys.getdefaultencoding(), 'replace')
+        raise TypeError("%s() got an unexpected keyword argument '%s'" %
+                        (f_name, unexpected))
+    unassigned = num_args - len([arg for arg in args if is_assigned(arg)])
+    if unassigned:
+        num_required = num_args - num_defaults
+        raise TypeError('%s() takes %s %d %s (%d given)' % (
+            f_name, 'at least' if defaults else 'exactly', num_required,
+            'arguments' if num_required > 1 else 'argument', num_total))
+    return arg2value
+
 # -------------------------------------------------- stack frame extraction
 
 Traceback = namedtuple('Traceback', 'filename lineno function code_context index')

Lib/test/test_inspect.py

+import re
 import sys
 import types
 import unittest
 import inspect
 import datetime
+from UserList import UserList
+from UserDict import UserDict
 
 from test.test_support import run_unittest, check_py3k_warnings
 
@@ -557,10 +560,197 @@ class TestClassesAndFunctions(unittest.TestCase):
         self.assertIn(('m1', 'method', D), attrs, 'missing plain method')
         self.assertIn(('datablob', 'data', A), attrs, 'missing data')
 
+class TestGetcallargsFunctions(unittest.TestCase):
+
+    # tuple parameters are named '.1', '.2', etc.
+    is_tuplename = re.compile(r'^\.\d+$').match
+
+    def assertEqualCallArgs(self, func, call_params_string, locs=None):
+        locs = dict(locs or {}, func=func)
+        r1 = eval('func(%s)' % call_params_string, None, locs)
+        r2 = eval('inspect.getcallargs(func, %s)' % call_params_string, None,
+                  locs)
+        self.assertEqual(r1, r2)
+
+    def assertEqualException(self, func, call_param_string, locs=None):
+        locs = dict(locs or {}, func=func)
+        try:
+            eval('func(%s)' % call_param_string, None, locs)
+        except Exception, ex1:
+            pass
+        else:
+            self.fail('Exception not raised')
+        try:
+            eval('inspect.getcallargs(func, %s)' % call_param_string, None,
+                 locs)
+        except Exception, ex2:
+            pass
+        else:
+            self.fail('Exception not raised')
+        self.assertIs(type(ex1), type(ex2))
+        self.assertEqual(str(ex1), str(ex2))
+
+    def makeCallable(self, signature):
+        """Create a function that returns its locals(), excluding the
+        autogenerated '.1', '.2', etc. tuple param names (if any)."""
+        code = ("lambda %s: dict(i for i in locals().items() "
+                "if not is_tuplename(i[0]))")
+        return eval(code % signature, {'is_tuplename' : self.is_tuplename})
+
+    def test_plain(self):
+        f = self.makeCallable('a, b=1')
+        self.assertEqualCallArgs(f, '2')
+        self.assertEqualCallArgs(f, '2, 3')
+        self.assertEqualCallArgs(f, 'a=2')
+        self.assertEqualCallArgs(f, 'b=3, a=2')
+        self.assertEqualCallArgs(f, '2, b=3')
+        # expand *iterable / **mapping
+        self.assertEqualCallArgs(f, '*(2,)')
+        self.assertEqualCallArgs(f, '*[2]')
+        self.assertEqualCallArgs(f, '*(2, 3)')
+        self.assertEqualCallArgs(f, '*[2, 3]')
+        self.assertEqualCallArgs(f, '**{"a":2}')
+        self.assertEqualCallArgs(f, 'b=3, **{"a":2}')
+        self.assertEqualCallArgs(f, '2, **{"b":3}')
+        self.assertEqualCallArgs(f, '**{"b":3, "a":2}')
+        # expand UserList / UserDict
+        self.assertEqualCallArgs(f, '*UserList([2])')
+        self.assertEqualCallArgs(f, '*UserList([2, 3])')
+        self.assertEqualCallArgs(f, '**UserDict(a=2)')
+        self.assertEqualCallArgs(f, '2, **UserDict(b=3)')
+        self.assertEqualCallArgs(f, 'b=2, **UserDict(a=3)')
+        # unicode keyword args
+        self.assertEqualCallArgs(f, '**{u"a":2}')
+        self.assertEqualCallArgs(f, 'b=3, **{u"a":2}')
+        self.assertEqualCallArgs(f, '2, **{u"b":3}')
+        self.assertEqualCallArgs(f, '**{u"b":3, u"a":2}')
+
+    def test_varargs(self):
+        f = self.makeCallable('a, b=1, *c')
+        self.assertEqualCallArgs(f, '2')
+        self.assertEqualCallArgs(f, '2, 3')
+        self.assertEqualCallArgs(f, '2, 3, 4')
+        self.assertEqualCallArgs(f, '*(2,3,4)')
+        self.assertEqualCallArgs(f, '2, *[3,4]')
+        self.assertEqualCallArgs(f, '2, 3, *UserList([4])')
+
+    def test_varkw(self):
+        f = self.makeCallable('a, b=1, **c')
+        self.assertEqualCallArgs(f, 'a=2')
+        self.assertEqualCallArgs(f, '2, b=3, c=4')
+        self.assertEqualCallArgs(f, 'b=3, a=2, c=4')
+        self.assertEqualCallArgs(f, 'c=4, **{"a":2, "b":3}')
+        self.assertEqualCallArgs(f, '2, c=4, **{"b":3}')
+        self.assertEqualCallArgs(f, 'b=2, **{"a":3, "c":4}')
+        self.assertEqualCallArgs(f, '**UserDict(a=2, b=3, c=4)')
+        self.assertEqualCallArgs(f, '2, c=4, **UserDict(b=3)')
+        self.assertEqualCallArgs(f, 'b=2, **UserDict(a=3, c=4)')
+        # unicode keyword args
+        self.assertEqualCallArgs(f, 'c=4, **{u"a":2, u"b":3}')
+        self.assertEqualCallArgs(f, '2, c=4, **{u"b":3}')
+        self.assertEqualCallArgs(f, 'b=2, **{u"a":3, u"c":4}')
+
+    def test_tupleargs(self):
+        f = self.makeCallable('(b,c), (d,(e,f))=(0,[1,2])')
+        self.assertEqualCallArgs(f, '(2,3)')
+        self.assertEqualCallArgs(f, '[2,3]')
+        self.assertEqualCallArgs(f, 'UserList([2,3])')
+        self.assertEqualCallArgs(f, '(2,3), (4,(5,6))')
+        self.assertEqualCallArgs(f, '(2,3), (4,[5,6])')
+        self.assertEqualCallArgs(f, '(2,3), [4,UserList([5,6])]')
+
+    def test_multiple_features(self):
+        f = self.makeCallable('a, b=2, (c,(d,e))=(3,[4,5]), *f, **g')
+        self.assertEqualCallArgs(f, '2, 3, (4,[5,6]), 7')
+        self.assertEqualCallArgs(f, '2, 3, *[(4,[5,6]), 7], x=8')
+        self.assertEqualCallArgs(f, '2, 3, x=8, *[(4,[5,6]), 7]')
+        self.assertEqualCallArgs(f, '2, x=8, *[3, (4,[5,6]), 7], y=9')
+        self.assertEqualCallArgs(f, 'x=8, *[2, 3, (4,[5,6])], y=9')
+        self.assertEqualCallArgs(f, 'x=8, *UserList([2, 3, (4,[5,6])]), '
+                                 '**{"y":9, "z":10}')
+        self.assertEqualCallArgs(f, '2, x=8, *UserList([3, (4,[5,6])]), '
+                                 '**UserDict(y=9, z=10)')
+
+    def test_errors(self):
+        f0 = self.makeCallable('')
+        f1 = self.makeCallable('a, b')
+        f2 = self.makeCallable('a, b=1')
+        # f0 takes no arguments
+        self.assertEqualException(f0, '1')
+        self.assertEqualException(f0, 'x=1')
+        self.assertEqualException(f0, '1,x=1')
+        # f1 takes exactly 2 arguments
+        self.assertEqualException(f1, '')
+        self.assertEqualException(f1, '1')
+        self.assertEqualException(f1, 'a=2')
+        self.assertEqualException(f1, 'b=3')
+        # f2 takes at least 1 argument
+        self.assertEqualException(f2, '')
+        self.assertEqualException(f2, 'b=3')
+        for f in f1, f2:
+            # f1/f2 takes exactly/at most 2 arguments
+            self.assertEqualException(f, '2, 3, 4')
+            self.assertEqualException(f, '1, 2, 3, a=1')
+            self.assertEqualException(f, '2, 3, 4, c=5')
+            self.assertEqualException(f, '2, 3, 4, a=1, c=5')
+            # f got an unexpected keyword argument
+            self.assertEqualException(f, 'c=2')
+            self.assertEqualException(f, '2, c=3')
+            self.assertEqualException(f, '2, 3, c=4')
+            self.assertEqualException(f, '2, c=4, b=3')
+            self.assertEqualException(f, '**{u"\u03c0\u03b9": 4}')
+            # f got multiple values for keyword argument
+            self.assertEqualException(f, '1, a=2')
+            self.assertEqualException(f, '1, **{"a":2}')
+            self.assertEqualException(f, '1, 2, b=3')
+            # XXX: Python inconsistency
+            # - for functions and bound methods: unexpected keyword 'c'
+            # - for unbound methods: multiple values for keyword 'a'
+            #self.assertEqualException(f, '1, c=3, a=2')
+        f = self.makeCallable('(a,b)=(0,1)')
+        self.assertEqualException(f, '1')
+        self.assertEqualException(f, '[1]')
+        self.assertEqualException(f, '(1,2,3)')
+
+class TestGetcallargsMethods(TestGetcallargsFunctions):
+
+    def setUp(self):
+        class Foo(object):
+            pass
+        self.cls = Foo
+        self.inst = Foo()
+
+    def makeCallable(self, signature):
+        assert 'self' not in signature
+        mk = super(TestGetcallargsMethods, self).makeCallable
+        self.cls.method = mk('self, ' + signature)
+        return self.inst.method
+
+class TestGetcallargsUnboundMethods(TestGetcallargsMethods):
+
+    def makeCallable(self, signature):
+        super(TestGetcallargsUnboundMethods, self).makeCallable(signature)
+        return self.cls.method
+
+    def assertEqualCallArgs(self, func, call_params_string, locs=None):
+        return super(TestGetcallargsUnboundMethods, self).assertEqualCallArgs(
+            *self._getAssertEqualParams(func, call_params_string, locs))
+
+    def assertEqualException(self, func, call_params_string, locs=None):
+        return super(TestGetcallargsUnboundMethods, self).assertEqualException(
+            *self._getAssertEqualParams(func, call_params_string, locs))
+
+    def _getAssertEqualParams(self, func, call_params_string, locs=None):
+        assert 'inst' not in call_params_string
+        locs = dict(locs or {}, inst=self.inst)
+        return (func, 'inst,' + call_params_string, locs)
+
 def test_main():
-    run_unittest(TestDecorators, TestRetrievingSourceCode, TestOneliners,
-                 TestBuggyCases,
-                 TestInterpreterStack, TestClassesAndFunctions, TestPredicates)
+    run_unittest(
+        TestDecorators, TestRetrievingSourceCode, TestOneliners, TestBuggyCases,
+        TestInterpreterStack, TestClassesAndFunctions, TestPredicates,
+        TestGetcallargsFunctions, TestGetcallargsMethods,
+        TestGetcallargsUnboundMethods)
 
 if __name__ == "__main__":
     test_main()

Misc/NEWS

@@ -32,6 +32,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #3135: Add inspect.getcallargs, which binds arguments to a function like
+  a normal call.
+
 - Backwards incompatible change: Unicode codepoints line tabulation (0x0B) and
   form feed (0x0C) are now considered linebreaks, as specified in Unicode
   Standard Annex #14.  See issue #7643.