Python: Convert list element strings that are positive and negative integers to an int?

Question

I'm wracking my brain with this. I need to iterate through a nested list (a list of lists, so only one level of sublist) to check if an entry is a positive or negative integer. If it is, I need to convert it to an int. The catch is that some other list elements contain numbers, so I can't just convert a list element containing numbers to an int because I get an error.

I tried this:

aList = ['a3','orange','-1','33']    
for aLine in aList:
    for token in aLine:
        if token.isdecimal() == True:
            map(int, aLine)
        elif token in "0123456789" and token.isalpha() == False:
            map(int, aLine)

...Which did absolutely nothing to my list.

I'm hoping to get this kind of output:

['a3', 'orange', -1, 33]

Answer 1

An easy way to check if a string s is an integer is by doing s.lstrip('+-').isdigit() which returns True/False . If the response is True you can cast it to int(s) which creates an integer.

You can create a new list from the responses or replace the item in the existing list if you have the index value. Here's a simple implementation.

aList = ['a3','orange','-1','33']
bList = []
for s in aList:
    if s.lstrip('+-').isdigit():
        bList.append(int(s.lstrip('+-'))
    else:
        bList.append(s)
print bList

The result of bList is as follows

>>> bList
['a3', 'orange', -1, 33]

Answer 2

This probably is not the most pythonic answer but it works:

assume

x = [['2','-5'],['a23','321','x12']]

the code is:

output = []
for row in x:
    temp = []
    for element in row:
        try:
            temp.append(int(element))
        except ValueError:
            temp.append(element)
    output.append(temp)

this gives you:

[[2, -5], ['a23', 321, 'x12']]

Answer 3

Anothere solution using list comprehension :

aList = ['a3', 'orange', '-1', '33']
results = [int(i) if i.lstrip('+-').isdigit() else i for i in aList]
print results

output:

['a3', 'orange', -1, 33]

Answer 4

Same can be achieved in one line using list comprehension. ( Let me know if you need explanation)

aList = ['a3', '14', 'orange', '-1', '33', '0']

print([int(x) if x.lstrip('-').isnumeric() else x for x in aList ])

['a3', 14, 'orange', -1, 33, 0]