CODEWITHSUNDEEP
pythonpython-2.7
Salty
Salty

Reputation: 23

What is this python syntax trying to do?

I'm wondering what is actually trying to happen in the following line. Forgive me I'm new to python syntax, thanks for the help! 

Handlers[type(dbw_msg)](dbw_msg)

Where handlers = secondary: self.secondary_manage.handle.message

and dbw_msg = py_from_can(can_msg)

where py_from can is defined as

def py_from_can(can_msg):
try:
    if can_msg.ID in py_can_types:
        return py_can_types[can_msg.ID].py_from_can(can_msg)
except NotImplementedError:
    pass
return None

Upvotes: 2

Views: 74

Answers (1)

juanpa.arrivillaga
juanpa.arrivillaga

Reputation: 95948

So, without any other context, all we can say is:

Handlers[type(dbw_msg)](dbw_msg)

Handlers gets subscripted (i.e. the square-brackets) with type(db_msg). We can only assume this is some sort of mapping (a dict) where the keys are type objects.

Finally, the value that is returned by the subcription operation get's called, i.e. the () parens. So, Handlers is some mapping from type objects to a callable (e.g. functions).

So, for example:

>>> handlers = {int: lambda x: x**2, str: str.upper}    
>>> a = 8
>>> b = 'foo'
>>> handlers[type(a)](a)
64
>>> handlers[type(b)](b)
'FOO'

Note, str.upper is merely the .upper method from your normal strings, i.e.:

>>> "baz".upper() # note the call!
'BAZ'

Is the same as:

>>> str.upper("baz")
'BAZ'

And a lambda is merely a way to write anonymous functions. It is equivalent to:

def square(x):
    return x**2

Upvotes: 1

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