CODEWITHSUNDEEP
pythonlistenumeration
theMobDog
theMobDog

Reputation: 1389

Python: from list to enumerated list to pass to lambda reduce function

I am trying to pass a list of hex char, into a lambda function, reduce to calculate a total decimal value. I am not sure what I am doing wrong but the python interpreter wouldn't recognize list(enumerate(reversed(numList)) as a list of tuples.

  numList =  ['3', '0', 'e', 'f', 'e', '1']
  reduce(lambda sum,(up,x):sum+ int(x,16)*16**up,
         enumerate(reversed(numList)))

when I print out

  list(enumerate(reversed(numList))

It is a list of tuples.

  [(0, '1'), (1, 'e'), (2, 'f'), (3, 'e'), (4, '0'), (5, '3')]

But it spit our error: can only concatenate tuple (not "int") to tuple

UPDATE:

The code is now working with a minor addition ",0" added to the lambda

    reduce(lambda sum,(up,x):sum+ int(x,16)*16**up,
         list(enumerate(reversed(numList))),0)

I don't understand what that means. Also I am not sure what is the best way to approach this.

that means you make sure, that it starts with 0 instead of the first Argument - in this case (0,'1') - because otherwise the types dont match? – am2 1 min ago

.

the third argument you add is initializer. without it, the sum in first iteration will be (0,'1'). so you were trying to evaluate (0,'1')+int(x,16)*16**up which is invalid. – ymonad 14 mins ago

UPDATE 2:

reduce(lambda sum,(up,x):sum+ int(x,16)*16**up,enumerate(reversed(numList)),0)

is just as good and enumerate() returns iter and list(enumerate...) is redundant.

Marked it as solved.

Upvotes: 1

Views: 1158

Answers (1)

shx2
shx2

Reputation: 64318

You don't need to use the generic reduce function when all you really need is to calculate the sum.

This works and is vastly simpler:

sum( int(x,16)*16**up for up,x in enumerate(reversed(numList)) )

Also, I'm going to guess you already know you can do the exact same thing like this:

int(''.join(numList), 16)

Upvotes: 2

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