Inserting a string into a list of integers

0
votes

I am trying to make a script where a '-' is put in between all odd digits in a given number (ie 991453 would be 9-9-145-3), but for some reason python wont allow me to insert a str into a list of integers. The error I keep on getting is 'TypeError: not all arguments converted during string formatting'

My code:

def DashInsert(text):

    list_int = map(int, list(text))

    for i in xrange(len(list_int)-1):
        if (list_int[i] % 2 == 1) and (list_int[i+1] % 2 == 1):
           print i
           list_int.insert(i+1,'-')

    return list_int

Here is my actual input and error:

999472

0

Traceback (most recent call last):

File "DashInsert.py", line 17, in 

print DashInsert(string)

File "DashInsert.py", line 11, in DashInsert

if (list_int[i] % 2 == 1) and (list_int[i+1] % 2 == 1):

TypeError: not all arguments converted during string formatting

3
pythonlisttype-conversion
Please show the actual input and the actual error trace back. – thefourtheye
FYI this is happening because you are modifying (specifically, adding to) the list while you are iterating over it. This is almost never a good idea. I mean, look what you are doing. You turn everything to ints first, but then you find the one you want and you insert a string in the next position. Hence, next round your % is string formatting! – Two-Bit Alchemist
@Two-BitAlchemist I understand what you are saying but the if statement should not allow the inserted '-' to through right? So I dont understand why its not working – Ridwan Kazi
What? The insert takes place inside the if statement. The '-' can only be inserted if that expression evaluates to true. – Two-Bit Alchemist

3 Answers

1
votes

Your error is because you are modifying the list that you are iterating over. When you insert - into the list, that becomes the target of % and you get a TypeError.

In Python, % is an operator for string formatting and '-' is a string; that is why you get a less than clear error:

>>> '-' % 2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: not all arguments converted during string formatting

For strings you use % this way:

>>> 'x %s y %s %i' % ('and', 'is', 13)
'x and y is 13'

The fix to your code is to append to a separate list:

def DashInsert(s):

    list_int = map(int, s)

    rtr=[]

    for i, e in enumerate(list_int[0:-1]):
        rtr.append(str(e))
        if e % 2 == 1 and list_int[i+1] % 2 == 1:
           rtr.append('-')
    rtr.append(str(list_int[-1]))    

    return rtr
1
votes

You could do this through regex.

>>> import re
>>> s = 991453
>>> re.sub(r'(?<=[13579])(?=[13579])', r'-', str(s))
'9-9-145-3'
1
votes

I suspect this is horrible code but it works-

number = 991453

number_list = []
for i, item in enumerate(str(number)):
    try:
        if int(item) % 2 != 0 and int(str(number)[i + 1]) % 2 != 0:
            number_list.append(item + '-')
        else:
            number_list.append(item)
    except:
        number_list.append(item)
print(''.join(number_list))

Edit: Actually, there's no need to make a list so we can do this-

number = 991453

dash_number = ''
for i, item in enumerate(str(number)):
    try:
        if int(item) % 2 != 0 and int(str(number)[i + 1]) % 2 != 0:
            dash_number += item + '-'
        else:
            dash_number += item
    except:
        dash_number += item
print(dash_number)

Edit: Here's how to do it without the try/except.

number = 991453

dash_number = ''
for i, item in enumerate(str(number)[:-1]):
    if int(item) % 2 != 0 and int(str(number)[i + 1]) % 2 != 0:
        dash_number += item + '-'
    else:
        dash_number += item
dash_number += str(number)[-1]

print(dash_number)