Python's logical operators "sort circuit" execute

[bartonc]

By that I mean they stop evaluation at the first True part of the expression.
I use it often to replace an uninitialized object. Like this:

>>> aString = ""
>>> aString or "Hello, world"
'Hello, world'
>>> anObject = None
>>> anObject or range(5)
[0, 1, 2, 3, 4]
>>> anObject = dict(a=1)
>>> anObject or range(5)
{'a': 1}
>>> 

[Smygis]

This has other uses aswell.

>>> 1 == 2 and "True value" or "False value"
'False value'
>>> 1 == 1 and "True value" or "False value"
'True value'
>>> 1 == 1 and "" or "The 'True' value must evaluate to True" # or perhaps not?
"The 'True' value must evaluate to True"
>>> 1 == 2 and "The 'False' value does not." or ""
''
>>> 
 

Not that this is anything anyone uses often. But its nice to know.

[bvdet]

It is sometimes useful for function defaults:

def polarEllipse(a, res, quad=1, xAxis=False, yAxis=False, rot=0):
 
    xAxis = float(xAxis or a.Ra)
    yAxis = float(yAxis or a.p1.dist(a.p3))
    ..........

[Motoma]

Good tip. Did you mean for this to be an Article?

[bartonc]

Good tip. Did you mean for this to be an Article?

Shhhh... That's my secret to high post counts: Publish in the forum, get lots of replies, then decide it should be an article and copy it there.

[bartonc]

It is sometimes useful for function defaults:

def polarEllipse(a, res, quad=1, xAxis=False, yAxis=False, rot=0):
 
    xAxis = float(xAxis or a.Ra)
    yAxis = float(yAxis or a.p1.dist(a.p3))
    ..........

Very useful!

I'm currently reading data from an RDBMS and storing to legacy text files (ongoing support for the predecessor of my project). The database may have empty fields, which are returned as None. The text file needs empty strings. So:

>>> field1 = None
>>> field2 = None
>>> ", ".join([str(field1 or ""), str(field2 or "")])

', '

>>> field2 = 7.6
>>> ", ".join([str(field1 or ""), str(field2 or "")])
', 7.6'
>>>