I want to convert this existing code to use pattern matching:
if isinstance(x, int):
pass
elif isinstance(x, str):
x = int(x)
elif isinstance(x, (float, Decimal)):
x = round(x)
else:
raise TypeError('Unsupported type')
How do you write isinstance
checks with pattern matching, and how do you test against multiple possible types like (float, Decimal)
at the same time?
Here's the equivalent code using match and case:
match x:
case int():
pass
case str():
x = int(x)
case float() | Decimal():
x = round(x)
case _:
raise TypeError('Unsupported type')
PEP 634 specifies that isinstance() checks are performed with class patterns. To check for an instance of str, write case str(): ...
. Note that the parentheses are essential. That is how the grammar determines that this is a class pattern.
To check multiple classes at a time, PEP 634 provides an or-pattern using the |
operator. For example, to check whether an object is an instance of float or Decimal, write case float() | Decimal(): ...
. As before, the parentheses are essential.
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