Python change type of whole list?

Question

I would like to do something like this

def foo(x,dtype=long):
   return magic_function_changing_listtype_to_dtype(x)

i.e. a list full of str to a list full of int

any easy way to do it for nested lists, i.e. change the type [[‘1’],[‘2’]] -> int

Asked By: bios

||

Source

Answer 1

Python 2:

map(int, ['1','2','3']) # => [1,2,3]

…

def foo(l, dtype=long):
    return map(dtype, l)

In Python 3, map() returns a map object, so you need to convert it to a list:

list(map(int, ['1','2','3'])) # => [1,2,3]

…

def foo(l, dtype=long):
    return list(map(dtype, l))

Answered By: Dan D.

Answer 2

str_list = ['1', '2', '3']
int_list = map(int, str_list)
print int_list # [1, 2, 3]

Answered By: Cat Plus Plus

Answer 3

def intify(iterable):
    result = []
    for item in iterable:
        if isinstance(item, list):
            result.append(intify(item))
        else:
            result.append(int(item))
    return result

works for arbitrarily deeply nested lists:

>>> l = ["1", "3", ["3", "4", ["5"], "5"],"6"]
>>> intify(l)
[1, 3, [3, 4, [5], 5], 6]

Answered By: Tim Pietzcker

Answer 4

List comprehensions should do it:

a = ['1','2','3']
print [int(s) for s in a]   # [1, 2, 3]]

Nested:

a = [['1', '2'],['3','4','5']]
print [[int(s) for s in sublist] for sublist in a]   # [[1, 2], [3, 4, 5]]

Answered By: Steven Rumbalski

Answer 5

Here is a fairly simple recursive function for converting nested lists of any depth:

def nested_change(item, func):
    if isinstance(item, list):
        return [nested_change(x, func) for x in item]
    return func(item)

>>> nested_change([['1'], ['2']], int)
[[1], [2]]
>>> nested_change([['1'], ['2', ['3', '4']]], int)
[[1], [2, [3, 4]]]

Answered By: Andrew Clark

Answer 6

a=input()#taking input as string. Like this-10 5 7 1(in one line)
a=a.split()#now splitting at the white space and it becomes ['10','5','7','1']
#split returns a list
for i in range(len(a)):
    a[i]=int(a[i]) #now converting each item of the list from string type
print(a)  # to int type and finally print list a

Answered By: Yash

Answer 7

Just as a comment to the answers here which use map. In Python 3 this wouldn’t work – something like map(int, ['1','2','3']) will not return [1,2,3] but a map object. To get the actual list object one needs to do list(map(int, ['1','2','3']))

Answered By: tsando

Python change type of whole list?

Question:

Answers: