#!/usr/bin/env python
# -*- coding: utf-8 -*-
NOVALUE = object()
class Maybe(object):
_has_value = False
_value = None
def __init__(self, value):
if value is not NOVALUE:
self._has_value = True
self._value = value
def __nonzero__(self):
return self.has_value
@property
def has_value(self):
return self._has_value
@property
def value(self):
return self._value
# optional sugar factories
def Some(value):
return Maybe(value)
def NoValue():
return Maybe(NOVALUE)
if __name__ == "__main__":
class MaybeSupportingRepository(object):
def __init__(self, *args):
self._d = dict(args)
def get(self, key):
return Maybe(self._d.get(key, NOVALUE))
repo = MaybeSupportingRepository( ("a", 1), ("b", 2), ("c", 3) )
key = "x"
maybe_v = repo.get(key)
if maybe_v:
print "There's a value for %s: %s" % (key, maybe_v.value)
else:
print "There's no value for %s" % key
key = "a"
maybe_v = repo.get(key)
if maybe_v.has_value:
print "There's a value for %s: %s" % (key, maybe_v.value)
else:
print "There's no value for %s" % key
Diff to Previous Revision
--- revision 1 2010-05-29 12:16:25
+++ revision 2 2010-07-21 11:08:11
@@ -1,11 +1,13 @@
#!/usr/bin/env python
# -*- coding: utf-8 -*-
+
+NOVALUE = object()
class Maybe(object):
_has_value = False
_value = None
def __init__(self, value):
- if value is not None:
+ if value is not NOVALUE:
self._has_value = True
self._value = value
@@ -25,7 +27,7 @@
return Maybe(value)
def NoValue():
- return Maybe(None)
+ return Maybe(NOVALUE)
if __name__ == "__main__":
class MaybeSupportingRepository(object):
@@ -33,7 +35,7 @@
self._d = dict(args)
def get(self, key):
- return Maybe(self._d.get(key))
+ return Maybe(self._d.get(key, NOVALUE))
repo = MaybeSupportingRepository( ("a", 1), ("b", 2), ("c", 3) )
