Python：列表列表，从字符串更改为整数

Question

x =[['+1', '+2', '+3', '+4', '+5', '+6']] 

y = [['+1', '-3', '-6', '-5'], ['+2', '-4']]

Is there anyway to change my list of lists from Strings to Integers?

I tried

def changy(foo):
    new = []
    for i in xrange(len(foo)):
        r = map(int, foo[i])
        new.append(r)
    return new
changy(x)

when I run

print changy(y)

my output is exactly what I want

[[1, -3, -6, -5], [2, -4]]

whenever I run x I get

ValueError: invalid literal for int() with base 10: '+'

Any help is appreciated

Answer 1

ValueError: invalid literal for int() with base 10: '+' means that you're first iterating the main list, then the nested list and then the characters in the string itself; that's one level "too far"/deep.

You can use a two-dimensional list comprehension. int() correctly interprets "+" and "-" as meaning positive and negative numbers:

>>> y = [['+1', '-3', '-6', '-5'], ['+2', '-4']]
>>> [[int(d) for d in z] for z in y]
[[1, -3, -6, -5], [2, -4]]
>>> 

You can use map in this way as well:

>>> y = [['+1', '-3', '-6', '-5'], ['+2', '-4']]
>>> [map(int,z) for z in y]
[[1, -3, -6, -5], [2, -4]]
>>> 

Answer 2

def changy(n):
    return [[int(d) for d in z] for z in n]

print changy(x)    
[[1, 2, 3, 4, 5, 6]]

print changy(y)
[[1, -3, -6, -5], [2, -4]]

n = (a nested list)

the above comment helped me realized I was iterating to far into my list.

This function helped me change my String nested lists to Integer nested lists.