Python: try statement single line

Question

Is there a way in python to turn a try/except into a single line?

something like...

b = 'some variable'
a = c | b #try statement goes here

Where b is a declared variable and c is not... so c would throw an error and a would become b...

Answer 1

There is no way to compress a try/except block onto a single line in Python.

Also, it is a bad thing not to know whether a variable exists in Python, like you would in some other dynamic languages. The safer way (and the prevailing style) is to set all variables to something. If they might not get set, set them to None first (or 0 or '' or something if it is more applicable.)

---

If you do assign all the names you are interested in first, you do have options.

• The best option is an if statement.

  c = None
  b = [1, 2]
  
  
  if c is None:
      a = b
  else:
      a = c
  

• The one-liner option is a conditional expression.

  c = None
  b = [1, 2]
  a = c if c is not None else b
  

• Some people abuse the short-circuiting behavior or or to do this. This is error prone so I never use it.

  c = None
  b = [1, 2]
  a = c or b
  

  consider the following case though

  c = []
  b = [1, 2]
  a = c or b
  

  in this case a probably should be [] but it is [1, 2] because [] is false in a boolean context. Because there are lots of values that can be false, I don't use the or trick. (This is the same problem people run into when they say if foo: when they mean if foo is not None:.)

Answer 2

You mentioned that you're using django. If it makes sense for what you're doing you might want to use:

my_instance, created = MyModel.objects.get_or_create()

created will be True or False. Maybe this will help you.

Answer 3

You can do it by accessing the namespace dict using vars(), locals(), or globals(), whichever is most appropriate for your situation.

>>> b = 'some variable'
>>> a = vars().get('c', b)