Forums
Python is (in)famous for its "batteries included" approach to a standard library, but it's not that notable that it has plenty of standard data structures, like dicts. Nor is in surprising that dicts have all sorts of useful methods, like pop, which removes a key from the dict and returns its value.
Because you're here, reading this site, you'll also be unsurprised that this doesn't stop developers from re-implementing that built-in function, badly. Karen sends us this:
def parse_message(message):
def pop(key):
if key in data:
result = data[key]
del data[key]
return result
return ''
data = json.loads(message)
some_value = pop("some_key")
# <snip>...multiple uses of pop()...</snip>
Here, they create an inner method, and they exploit variable hoisting. While pop appears in the code before data is declared, all variable declarations are "hoisted" to the top. When pop references data, it's getting that from the enclosing scope. Which while this isn't a global variable, it's still letting a variable cross between two scopes, which is always messy.
Also, this pop returns a default value, which is also something the built-in method can do. It's just the built-in version requires you to explicitly pass the value, e.g.: some_value = data.pop("some_key", "")
Karen briefly wondered if this was a result of the Python 2 to 3 conversion, but no, pop has been part of dict for a long time. I wondered if this was just an exercise in code golf, writing a shorthand function, but even then- you could just wrap the built-in pop with your shorthand version (not that I'd recommend such a thing). No, I think the developer responsible simply didn't know the function was there, and just reimplemented a built-in method badly, as so often happens.