List to int in python

Question

I am wondering if there is a nice way to convert a list of digits to an integer in python. That is, if I have mylist = [1, 5, 9] I would like to do something like int(mylist) to get an output of 159. I am assuming that the input list simply has digits, and I want to use this to create a number. Currently the best I have is:

mylist = [1, 5, 9]
num = 0
for i in range(len(mylist)):
    num += mylist[i] * 10 ** (len(mylist) - i - 1)

Which should work alright, but feels too explicit. Is there a neater/nicer way to do this?

`num = int(''.join([str(item) for item in mylist]))` – roganjosh May 24 '20 at 23:47 — roganjosh, May 24 '20 at 23:47

score 1 · Answer 1 · answered May 24 '20 at 23:49

1

You might want to reconsider how your data got into that structure and fix that.

But you can easily combine it as a string and call int() on it:

int("".join(str(i) for i in mylist))

answered May 24 '20 at 23:49

monkut

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score 0 · Answer 2 · answered May 24 '20 at 23:45

0

Currently the best I can think of is:

mylist = [1, 5, 9]
num = 0
for i in range(len(mylist)):
    num += mylist[i] * 10 ** (len(mylist) - i - 1)

answered May 24 '20 at 23:45

Math chiller

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Isn't this the exact same code as in your question? – Chris May 24 '20 at 23:47
@Chris Yes it is. I just figured that since it accomplishes the task, I ought to add as answer. – Math chiller May 25 '20 at 15:30

score 0 · Answer 3 · answered May 24 '20 at 23:48

0

Try this:

list = [1, 2, 3]
string = ''
for num in list:
    string = string + str(num)
result = int(string)
print(result)

answered May 24 '20 at 23:48

CircuitSacul

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score 0 · Answer 4 · answered May 24 '20 at 23:51

0

The map function is generally faster. I used a lambda, but you could also just create your own function instead of a lambda.

mylist = [1, 5, 9]
N = len(mylist)
sum(list(map(lambda x : x[0]*10**(N-x[1]-1),  enumerate(mylist))))

answered May 24 '20 at 23:51

targetXING

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score 0 · Answer 5 · answered May 24 '20 at 23:51

0

Use functools.reduce:

from functools import reduce

assert reduce(lambda a, x: 10*a + x, [1,5,9]) == 159

This is a short way of implementing Horner's Method.

answered May 24 '20 at 23:51

chepner

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List to int in python

5 Answers5