Using default arguments when variable length arguments are present

Question

I want to default the parameter C to 20 if I don't supply any values.

How is this possible ?

functypes(1,2,,4,5,6,id='jijo',job='engineer')

I have tried this but it shows syntax error :

functypes(1,2,,4,5,6,)
                  ^
SyntaxError: invalid syntax

def functypes(a,b,c=20,*y,**Z):
    print("the values of a,b,c are",a,b,c)
    for y1 in y:
        print("The values in Y are",y1,",",end='')
    for z1,z2 in Z.items():
        print("The values in Z are",z1,z2)

The following call works fine :

functypes(1,2,,4,5,6,id='jijo',job='engineer')

sahasrara62 · Accepted Answer · 2019-05-21 09:12:04Z

2

change def functypes(a,b,c=20,*y,**Z): to def functypes(a,b,*y,c=20,**Z): this will mintain c and keep values as desired , since c is key-value pair need to add vefore key value

def functypes(a,b,*y,c=20,**Z):
    print("the values of a,b,c are",a,b,c)
    for y1 in y:
        print("The values in Y are",y1,",",end='\n')
    for z1,z2 in Z.items():
        print("The values in Z are",z1,z2)

functypes(1,2,3,4,5,6,id='jijo',job='engineer')

""" output 
the values of a,b,c are 1 2 20
The values in Y are 3 ,
The values in Y are 4 ,
The values in Y are 5 ,
The values in Y are 6 ,
The values in Z are id jijo
The values in Z are job engineer
"""

answered May 21, 2019 at 9:12

sahasrara62

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Comments

Thuvarakan Tharmarajasingam · Accepted Answer · 2019-05-21 09:12:23Z

2

Putting the default arg after *args makes it a keyword-only argument which can be only specified by name, not by position.

def functypes(a,b,*y,c=20,**Z):
    print("the values of a,b,c are",a,b,c)
    for y1 in y:
        print("The values in Y are",y1,",",end='')
    for z1,z2 in Z.items():
        print("The values in Z are",z1,z2)

functypes(1,4,5,6,7,8,c=9,id='jijo',job='engineer') #take c as 9
functypes(1,4,5,6,7,8,id='jijo',job='engineer') #take c as 20

answered May 21, 2019 at 9:12

Thuvarakan Tharmarajasingam

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Comments

Serge Ballesta · Accepted Answer · 2019-05-21 09:13:56Z

You cannot. Python does not allow to pass an explicit empty parameter. Said differently you are not allowed to write consecutive commas (,,) in a function call, so you can only pass keyword arguments after an empty parameter

A common idiom is to use a None value:

def functypes(a,b,c=None,*y,**Z):
    if c is None: c=20
    print("the values of a,b,c are",a,b,c)
    for y1 in y:
        print("The values in Y are",y1,",",end='')
    for z1,z2 in Z.items():
        print("The values in Z are",z1,z2)

You can then use: functypes(1,2,None,4,5,6,id='jijo',job='engineer')

Alternatively you can pass explicitely the y argument as a keyword: functypes(1,2,y=[4,5,6],id='jijo',job='engineer') but it really looks like an anti-pattern...

TomG · Accepted Answer · 2019-05-21 09:25:15Z

0

Somebody posted and This worked.

functypes(1,2,*[3,4,5,6],id='jijo',job='engineer')

answered May 21, 2019 at 9:25

TomG

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1 Comment

sahasrara62 Over a year ago

functypes(1,2,*[3,4,5,6],id='jijo',job='engineer') it is same as functypes(1,2,3,4,5,6,id='jijo',job='engineer') just here you have unpacked list given in abouve you have a list that cintain all dat a and uit is unpacked insidde function call

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