Ternary operator alternative in Ptyhon

[kretik]

I'm sure this is a popular one, but after Googling for a while I
couldn't figure out how to pull this off.

Let's say I have this initializer on a class:

def __init__(self, **params):

I'd like to short-circuit the assignment of class field values passed in
this dictionary to something like this:

self.SomeField = \
params.has_key("mykey") ? params["mykey"] : None)

Obviously I know this is not actual Python syntax, but what would be the
equivalent? I'm trying to avoid this, basically:

if params.has_key("mykey"):
self.SomeField = params["mykey"]
else:
self.SomeField = None

This is not a big deal of course, but I guess my main goal is to try and
figure out of I'm not missing something more esoteric in the language
that lets me do this.

Thanks in advance.

 

[Robert Lehmann]

I'm sure this is a popular one, but after Googling for a while I
couldn't figure out how to pull this off.

Let's say I have this initializer on a class:

def __init__(self, **params):

Why not ``__init__(self, mykey=None)`` in the first place?

I'd like to short-circuit the assignment of class field values passed in
this dictionary to something like this:

self.SomeField = \
params.has_key("mykey") ? params["mykey"] : None)

Obviously I know this is not actual Python syntax, but what would be the
equivalent? I'm trying to avoid this, basically:

if params.has_key("mykey"):
self.SomeField = params["mykey"]
else:
self.SomeField = None

This is not a big deal of course, but I guess my main goal is to try and
figure out of I'm not missing something more esoteric in the language
that lets me do this.

Thanks in advance.

You're lucky -- Python 2.5 just grew a ternary if-construct. You'd use it
like that::

self.SomeField = params["mykey"] if "mykey" in params else None
# or, generically: TRUE if CONDITION else FALSE

Notice the use of the `in` operator, which is recommended over
`dict.has_key`.

HTH,

 

[William Heymann]

if params.has_key("mykey"):
self.SomeField = params["mykey"]
else:
self.SomeField = None

self.SomeField = parms.get('mykey', None)

This looks like what you want and it is also simpler because you don't deal
with checking if the key exists.

 

[Gary Herron]

I'm sure this is a popular one, but after Googling for a while I
couldn't figure out how to pull this off.

Let's say I have this initializer on a class:

def __init__(self, **params):

I'd like to short-circuit the assignment of class field values passed
in this dictionary to something like this:

self.SomeField = \
params.has_key("mykey") ? params["mykey"] : None)

For years, Python did not have such a thing, but recent versions support
the syntax
a if c else b

In spite of the odd ordering of that parts, they are executed (or not)
just as you like.
self.SomeField = params["mykey"] if params.has_key("mykey") else None


Gary Herron

Obviously I know this is not actual Python syntax, but what would be
the equivalent? I'm trying to avoid this, basically:

if params.has_key("mykey"):
self.SomeField = params["mykey"]
else:
self.SomeField = None

This is not a big deal of course, but I guess my main goal is to try
and figure out of I'm not missing something more esoteric in the
language that lets me do this.

Thanks in advance.

 

[jeremie fouche]

kretik a écrit :

I'm sure this is a popular one, but after Googling for a while I
couldn't figure out how to pull this off.

I'd like to short-circuit the assignment of class field values passed in
this dictionary to something like this:

self.SomeField = \
params.has_key("mykey") ? params["mykey"] : None)

Obviously I know this is not actual Python syntax, but what would be the
equivalent? I'm trying to avoid this, basically:

if params.has_key("mykey"):
self.SomeField = params["mykey"]
else:
self.SomeField = None

This is not a big deal of course, but I guess my main goal is to try and
figure out of I'm not missing something more esoteric in the language
that lets me do this.

You can also use :
self.SomeField = params.has_key("mykey") and params["mykey"] or None

But it's not easy to read

 

[kretik]

Thank you everyone. I ended up implementing the dict.get() method, which
seems "cleaner", but I'll keep the (x if y else z) syntax in mind. I
didn't know it existed, I guess it's what I was looking for to begin with.

Thanks again!