Overloading "if object" unary operator

[Sarcastic Zombie]

Good morning,

If I have a class

class A:
__init__(id)
self.id = id

is there any way to overload the 'if' unary usage to detect if a
variable has a value?

For example, in the code:

a = A(56)
if a:
print "Hoo hah!"

how can I insure that the if will come back true and fire off the print
if and only if self.id is defined? I want to do this in an overloaded,
generic way, if possible; I know that I could test for a.id.

Thanks so much!

-Jason Ledbetter

 

[Roberto Bonvallet]

For example, in the code:

a = A(56)
if a:
print "Hoo hah!"

how can I insure that the if will come back true and fire off the print
if and only if self.id is defined? I want to do this in an overloaded,
generic way, if possible; I know that I could test for a.id.

Define a method called __nonzero__ that returns True or False.

 

[Peter Otten]

is there any way to overload the 'if' unary usage to detect if a
variable has a value?

Define a __nonzero__() or __len__() method.

Peter

 

[Sarcastic Zombie]

Peter

Thanks to both of you, it worked perfectly. I must have missed it in
the documentation somehow.

-Jason Ledbetter

 

[Fredrik Lundh]

If I have a class

class A:
__init__(id)
self.id = id

is there any way to overload the 'if' unary usage to detect if a
variable has a value?

http://effbot.org/pyref/__nonzero__

</F>