ragzputin ragzputin - 4 months ago 16
Python Question

If statement with no logical operators in python

I have the following python code:

value = 1.9

if value:
#do something
else:
#do something else


What happens here? I can't understand this because
value
is not Boolean.

Answer

Python has a concept of truthy-ness where non-Boolean values are basically "coerced" into Boolean ones, as shown here:

4.1 Truth value testing

Any object can be tested for truth value, for use in an if or while condition or as operand of the Boolean operations below. The following values are considered false:

  • None
  • False
  • zero of any numeric type, for example, 0, 0.0, 0j.
  • any empty sequence, for example, '', (), [].
  • any empty mapping, for example, {}.
  • instances of user-defined classes, if the class defines a __bool__() or __len__() method, when that method returns the integer zero or bool value False.

All other values are considered true - so objects of many types are always true.

Operations and built-in functions that have a Boolean result always return 0 or False for false and 1 or True for true, unless otherwise stated. (Important exception: the Boolean operations or and and always return one of their operands.)

Bottom line is that 1.9 comes under the "All other values are considered true" clause since it matches none of the values that would be considered false. The closest it comes is the third one (numeric type) but, since it's non-zero, it doesn't quite get there.