Add index variable with more than one loop variable Python-CodePudding

When running a one variable loop, adding an index variable is easy:

a = ( (2,3), (7,9) )
for i,v in enumerate( a ):
    print( v )
    print( i )

Yields:

(2, 3)
0
(7, 9)
1

Trying to generate a two-variable loop works well too:

for c,v in enumerate( a ):
    print( c )
    print( v )

Yields:

0
(2, 3)
1
(7, 9)

However, adding an index, via enumerate, for 3 loop variables, does not work:

for i,c,v in enumerate( a ):
    print( c )

Yields:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: not enough values to unpack (expected 3, got 2)

CodePudding user response：

enumerate returns an iterator with pairs, never triples. For this particular input data, the second member of such a pair is a pair itself. So there is nesting. You should unpack that structure using the same nesting:

for i, (c, v) in enumerate( a ):
    print(f"i={i} c={c} v={v}")