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

Patch by George Sakkis

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')