"""deferred_default_arg module
Deferred is singleton to be used in place of None as the sentinel
for deferred default arguments.
"""
import inspect
class DeferredType: pass
Deferred = DeferredType()
def handle_deferred(f, name, fname=None):
"""Turn the singleton Deferred object into a default arg.
f - the function to which you will pass the argument.
name - the local name that will be passed as the argument.
fname - the argument name of f. If this is not passed, the name
is used.
If the argument of f() doesn't have a default value, raise a
TypeError. This is what would normally happen if you tried to call
f() without passing that argument. That's effectively what you are
doing in that situation when passing Deferred.
This function is a lot simpler if you use the PEP 362 function
signature object.
"""
if not fname:
fname = name
val = inspect.stack()[1][0].f_locals[name]
if val is not Deferred:
return val
notkwonlycount = f.__code__.co_argcount - f.__code__.co_kwonlyargcount
if fname in f.__code__.co_varnames[notkwonlycount:]:
try:
return f.__kwdefaults__[fname]
except KeyError:
raise TypeError("Can't convert Deferred for {}".format(name))
default_names = f.__code__.co_varnames[
notkwonlycount - len(f.__defaults__):notkwonlycount]
try:
return f.__defaults__[default_names.index(fname)]
except ValueError:
raise TypeError("Can't convert Deferred for {}".format(name))
Diff to Previous Revision
--- revision 1 2011-07-15 03:13:02
+++ revision 2 2011-08-12 23:08:30
@@ -1,4 +1,9 @@
-"""deferred_default_arg module"""
+"""deferred_default_arg module
+
+Deferred is singleton to be used in place of None as the sentinel
+for deferred default arguments.
+
+"""
import inspect
@@ -7,17 +12,17 @@
def handle_deferred(f, name, fname=None):
- """Turn the singleton Deferred object into an default arg.
+ """Turn the singleton Deferred object into a default arg.
f - the function to which you will pass the argument.
name - the local name that will be passed as the argument.
fname - the argument name of f. If this is not passed, the name
is used.
- If the "fname" argument of "f" does not have a default value, raise
- a TypeError. This is what would happen if you tried to call "f"
- without passing that argument. That's effectively what you are
- doing when passing Deferred as that argument.
+ If the argument of f() doesn't have a default value, raise a
+ TypeError. This is what would normally happen if you tried to call
+ f() without passing that argument. That's effectively what you are
+ doing in that situation when passing Deferred.
This function is a lot simpler if you use the PEP 362 function
signature object.
