?: in Python

[Andy Leszczynski]

How can do elegantly in Python:

if condition:
a=1
else:
a=2

like in C:

a=condition?1:2

 

[Andy Leszczynski]

How can do elegantly in Python:

if condition:
a=1
else:
a=2

like in C:

a=condition?1:2

There are tons of threads on this newsgroup and in the python-dev mailing
list about a ternary operator. There's also a PEP AFAIK.

I like this:

In [1]:switch = True

In [2]:a = (1, 2)[switch]

In [3]rint a
2

Like it too, thx. Switch does not have to be bool, so it is more
powerfull than ?:.

A.

 

[Lawrence Oluyede]

How can do elegantly in Python:

if condition:
a=1
else:
a=2

like in C:

a=condition?1:2

There are tons of threads on this newsgroup and in the python-dev mailing
list about a ternary operator. There's also a PEP AFAIK.

I like this:

In [1]:switch = True

In [2]:a = (1, 2)[switch]

In [3]rint a
2

 

[gene tani]

How can do elegantly in Python:

if condition:
a=1
else:
a=2

like in C:

a=condition?1:2

google for ternary operator

http://www.python.org/doc/faq/programming.html#is-there-an-equivalent-of-c-s-ternary-operator
http://www.norvig.com/python-iaq.html

http://mail.python.org/pipermail/python-list/2005-November/310854.html
http://www.python.org/peps/pep-0308.html

http://diveintopython.org/power_of_introspection/and_or.html#d0e9975
http://aspn.activestate.com/ASPN/Python/Cookbook/Recipe/52310

 

[Bengt Richter]

How can do elegantly in Python:

if condition:
a=1
else:
a=2

like in C:

a=condition?1:2

There are tons of threads on this newsgroup and in the python-dev mailing
list about a ternary operator. There's also a PEP AFAIK.

I like this:

In [1]:switch = True

In [2]:a = (1, 2)[switch]

In [3]rint a
2

You won't like it in a case like
a = (2**20**20, 2)[switch]
or
a = (m/n, sys.maxint)[n==0]
the point is that if/else only evaluates
the expression in one branch, as with C ternary.

You're right, there is a PEP and a ternary expression
coming to python though.

Regards,
Bengt Richter

 

[Peter Hansen]

There are tons of threads on this newsgroup and in the python-dev mailing
list about a ternary operator. There's also a PEP AFAIK.

I like this:

In [1]:switch = True

In [2]:a = (1, 2)[switch]

In [3]rint a
2

Like it too, thx. Switch does not have to be bool, so it is more
powerfull than ?:.

Actually, if "switch" is neither bool nor a number that equals 0 or 1,
you'll have trouble... using bool(switch) instead would do what you
thought that did, I guess.

-Peter

 

[Steven D'Aprano]

How can do elegantly in Python:

if condition:
a=1
else:
a=2

like in C:

a=condition?1:2

I thought you wanted to do it *elegantly*?

Your first solution is perfectly elegant to my eyes, unlike that horrible
C syntax.

 

[bonono]

How can do elegantly in Python:

if condition:
a=1
else:
a=2

like in C:

a=condition?1:2

a=(condition and [1] or [2])[0]

For this simple snippet, I don't think it is better than if/else, But
you can use it in map/reduce or list comprehension/generator expression.

 

[Andy Leszczynski]

I thought you wanted to do it *elegantly*?

Your first solution is perfectly elegant to my eyes, unlike that horrible
C syntax.

I can tell you what is not elegant in the if else: approach. It is
logically a one operation while you are forced to use varaible "a"
twice. Fundamental flaw IMO.

A.

 

[Steven Bethard]

How can do elegantly in Python:

if condition:
a=1
else:
a=2

like in C:

a=condition?1:2

Step (1): Wait for Python 2.5[1]
Step (2): Write the code::

a = 1 if condition else 2

STeVe

[1]http://www.python.org/peps/pep-0308.html

 

[Dave Hansen]

How can do elegantly in Python:

if condition:
a=1
else:
a=2

like in C:

a=condition?1:2

There are tons of threads on this newsgroup and in the python-dev mailing
list about a ternary operator. There's also a PEP AFAIK.

I like this:

In [1]:switch = True

In [2]:a = (1, 2)[switch]

In [3]rint a
2

Note, however, you have the logic backwards. To duplicate the
functionality of the OP's example, you need

a = (2,1)[condition]

or

a = (1,2)[not condition]

Regards,
-=Dave

 

[Steven D'Aprano]

I can tell you what is not elegant in the if else: approach. It is
logically a one operation while you are forced to use varaible "a"
twice. Fundamental flaw IMO.

"Logically" one operation?

def twenty_countries_in_seven_days_bus_tour():
...
if today() == Monday:
write_postcode_to_mother("We must be in Belgium.")
else:
get_back_on_the_bus("Not again!")
...


if...else expressions with a single operation are just a special case.
Perhaps a common special case, but still a special case.

 

[Andrew Koenig]

How can do elegantly in Python:

if condition:
a=1
else:
a=2

I believe that before long Python will support

a=1 if condition else 2

 

[Kent Johnson]

How can do elegantly in Python:

if condition:
a=1
else:
a=2

like in C:

a=condition?1:2

a = condition and A or B
is concise but will fail if A can evaluate as false, e.g.
a = condition and None or 2 # won't do what you want

I tend to use 'condition and A or B' if I'm sure A won't be false, otherwise just write
out the if / else.

Kent

 

[Andy Leszczynski]

"Logically" one operation?

def twenty_countries_in_seven_days_bus_tour():
...
if today() == Monday:
write_postcode_to_mother("We must be in Belgium.")
else:
get_back_on_the_bus("Not again!")
...


if...else expressions with a single operation are just a special case.
Perhaps a common special case, but still a special case.

First:
"Special cases aren't special enough to break the rules.
Although practicality beats purity."


Second, let's look at again:

>if condition:
> a=1
>else:
> a=2

The primer meaning behind that is that I want to assign something to a.
What I want to assign is secondary issue. I do not like C syntax of ?:
either but I think it is just practical and self-explanatory.

A.