argparse: Add support for custom argument types.

python-stdlib/argparse/argparse.py

@@ -10,29 +10,39 @@ class _ArgError(BaseException):
     pass
 
 
+class ArgumentTypeError(BaseException):
+    pass
+
+
 class _Arg:
-    def __init__(self, names, dest, action, nargs, const, default, help):
+    def __init__(self, names, dest, action, nargs, const, default, help, type):
         self.names = names
         self.dest = dest
         self.action = action
         self.nargs = nargs
         self.const = const
         self.default = default
         self.help = help
+        self.type = type
+
+    def _apply(self, optname, arg):
+        if self.type:
+            try:
+                return self.type(arg)
+            except (ArgumentTypeError, TypeError, ValueError) as e:
+                raise _ArgError("invalid value for %s: %s (%s)" % (optname, arg, str(e)))
+        return arg
 
     def parse(self, optname, args):
         # parse args for this arg
         if self.action == "store":
             if self.nargs is None:
                 if args:
-                    return args.pop(0)
+                    return self._apply(optname, args.pop(0))
                 else:
                     raise _ArgError("expecting value for %s" % optname)
             elif self.nargs == "?":
-                if args:
-                    return args.pop(0)
-                else:
-                    return self.default
+                return self._apply(optname, args.pop(0) if args else self.default)
             else:
                 if self.nargs == "*":
                     n = -1
@@ -52,7 +62,7 @@ def parse(self, optname, args):
                         else:
                             break
                     else:
-                        ret.append(args.pop(0))
+                        ret.append(self._apply(optname, args.pop(0)))
                         n -= 1
                 if n > 0:
                     raise _ArgError("expecting value for %s" % optname)
@@ -103,6 +113,10 @@ def add_argument(self, *args, **kwargs):
                 dest = args[0]
             if not args:
                 args = [dest]
+        arg_type = kwargs.get("type", None)
+        if arg_type is not None:
+            if not callable(arg_type):
+                raise ValueError("type is not callable")
         list.append(
             _Arg(
                 args,
@@ -112,6 +126,7 @@ def add_argument(self, *args, **kwargs):
                 const,
                 default,
                 kwargs.get("help", ""),
+                arg_type,
             )
         )
 
@@ -176,7 +191,9 @@ def _parse_args(self, args, return_unknown):
         arg_vals = []
         for opt in self.opt:
             arg_dest.append(opt.dest)
-            arg_vals.append(opt.default)
+            arg_vals.append(
+                opt._apply(opt.dest, opt.default) if isinstance(opt.default, str) else opt.default
+            )
 
         # deal with unknown arguments, if needed
         unknown = []

python-stdlib/argparse/manifest.py

@@ -1,4 +1,4 @@
-metadata(version="0.4.0")
+metadata(version="0.5.0")
 
 # Originally written by Damien George.
 

python-stdlib/argparse/test_argparse.py

@@ -66,3 +66,47 @@
 args, rest = parser.parse_known_args(["a", "b", "c", "-b", "2", "--x", "5", "1"])
 assert args.a == ["a", "b"] and args.b == "2"
 assert rest == ["c", "--x", "5", "1"]
+
+
+class CustomArgType:
+    def __init__(self, add):
+        self.add = add
+
+    def __call__(self, value):
+        return int(value) + self.add
+
+
+parser = argparse.ArgumentParser()
+parser.add_argument("-a", type=int)
+args = parser.parse_args(["-a", "123"])
+assert args.a == 123
+parser.add_argument("-b", type=str)
+args = parser.parse_args(["-b", "string"])
+assert args.b == "string"
+parser.add_argument("-c", type=CustomArgType(1))
+args = parser.parse_args(["-c", "123"])
+assert args.c == 124
+try:
+    parser.add_argument("-d", type=())
+    assert False
+except ValueError as e:
+    assert "not callable" in str(e)
+parser.add_argument("-d", type=int, nargs="+")
+args = parser.parse_args(["-d", "123", "124", "125"])
+assert args.d == [123, 124, 125]
+parser.add_argument("-e", type=CustomArgType(1), nargs="+")
+args = parser.parse_args(["-e", "123", "124", "125"])
+assert args.e == [124, 125, 126]
+parser.add_argument("-f", type=CustomArgType(1), nargs="?")
+args = parser.parse_args(["-f", "123"])
+assert args.f == 124
+parser.add_argument("-g", type=CustomArgType(1), default=1)
+parser.add_argument("-i", type=CustomArgType(1), default="1")
+args = parser.parse_args([])
+assert args.g == 1
+assert args.i == 2
+parser.add_argument("-j", type=CustomArgType(1), default=1)
+args = parser.parse_args(["-j", "3"])
+assert args.g == 1
+assert args.i == 2
+assert args.j == 4