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Python function parameter matching model general rule keyword-only parameter

Overview

Python3's collation of function parameters is more general, namely the Python3 keyword-only parameter, which is a parameter that must be passed only by keyword and not populated with a positional parameter. This rule is useful in dealing with more than one parameter of a person.

Keyword-only

Kword_only (1,2,3, cyste4) print ('-'* 20) kword_only (axi1, cyste3)

Example result:

1 (2, 3) 4-1 () 3

All parameters after * args need to be passed using keywords in the call, otherwise an exception will be thrown.

Def kword_only (a, * b, c): print (a, b, c) kword_only (1,2,3)

Abnormal result:

Kword_only (1,2,3) TypeError: kword_only () missing 1 required keyword-only argument:'c'

We can also use a * character in the parameter list to indicate that the function will not accept a parameter list of variable length, but requires that the parameters that follow * need to be passed using keyword arguments.

Def kword_only (a, *, b, c): print (a, b, c) kword_only (1, baux2, cyste3) print ('-'* 20) kword_only (baux2, cyste3, axi1)

Example result:

1 2 3-1 2 3

We can see that a can be passed using positional parameters, but b and c must be passed through keyword arguments, otherwise an exception will be thrown.

Def kword_only (a, *, b, c): print (a, b, c) kword_only (1,2,3)

Abnormal result:

Kword_only (1,2,3) TypeError: kword_only () takes 1 positional argument but 3 were given

Of course, we can use the default value for the keyword-only parameter, in this case a can still be passed through the position parameter or keyword parameter, while b and c are optional, of course, if you need to pass, you still need to use the keyword parameter to pass.

Def kword_only (a, *, bread2, cymb3): print (a, b, c) kword_only (1) print ('-'* 20) kword_only (axi1) print ('-'* 20) kword_only (bread22, cymb33, aq11)

Example result:

1 2 3-1 2 3-11 22 33

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