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Take default value for Enum from allowed values #13

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Take default value for Enum from allowed values #13

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10 changes: 8 additions & 2 deletions traitlets/traitlets.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1419,9 +1419,15 @@ def validate(self, obj, value):
class Enum(TraitType):
"""An enum that whose value must be in a given sequence."""

def __init__(self, values, default_value=None, **metadata):
def __init__(self, values, default_value=NoDefaultSpecified, allow_none=False, **metadata):
self.values = values
super(Enum, self).__init__(default_value, **metadata)
if default_value is NoDefaultSpecified:
if (not allow_none) and values:
# The first value in a list/tuple, or an arbitrary value from a set
default_value = next(iter(values))
else:
default_value = None
super(Enum, self).__init__(default_value, allow_none=allow_none, **metadata)
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@SylvainCorlay SylvainCorlay Apr 30, 2015

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You could also do

if default_value is NoDefaultSpecified:
    if self.values:
        default_value = next(iter(self.values))
    else:
        default_value  = Undefined

and have it all not depend and allow_none.


def validate(self, obj, value):
if value in self.values:
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