TypeError when using string.join() in Python

Question

I am writing a very simple function that, given a string as input, parses the string into sentences, reverses the words of each sentence, and returns the reversed sentences but in the given sentence order. I am struggling with the string.split() and string.join() built-in methods and am getting a TypeError when I run the following python program.

import string

def reverseSentences(str):
    senList = str.split('.')
    for i, item in enumerate(senList[:]):
        senList[i] = string.join(item.split(' ').reverse(), ' ')
    return string.join(senList, '.') + '.'

When I try to print a call to this function it gives me a generic TypeError. Thanks for enduring my n00bishness.

`string.join` is old cruft (and removed in newer Python versions) - use `' '.join(reversed(...))` — , Jun 19 '13 at 19:33

Rohit Jain · Answer 1 · 2013-06-19T19:35:01.257

2

item.split(' ').reverse() does not return the list, rather it does the reverse in place. So, your join is same as:

string.join(None, ' ')

Clearly a problem. You should rather use reversed() function:

string.join(reversed(item.split(' ')), ' ')

And rather than string.join function, use the method defined in string class in newer Python version.

' '.join(reversed(item.split(' '))

edited Jun 19 '13 at 19:35

answered Jun 19 '13 at 19:28

Rohit Jain

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score 1 · Accepted Answer · edited May 23 '17 at 12:06

1

Try

>> str = 'a1 b2'
>> ' '.join(x[::-1] for x in str.split())
'1a 2b'

In function form:

def reverseSentences(str):
  return ' '.join(x[::-1] for x in str.split())

Notice that x[::-1] is way faster than reversed() (Reverse a string in Python).

edited May 23 '17 at 12:06

Community

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answered Jun 19 '13 at 19:30

Felipe Hoffa

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I think, OP just needs - `' '.join(str.split()[::-1])`. You are reversing each word. – Rohit Jain Jun 19 '13 at 19:38
You are right! This description confused me "reverses the words of each sentence". And OP didn't give a example input/output. It was fun to quick code anyway :) – Felipe Hoffa Jun 19 '13 at 19:40

score 0 · Answer 3 · answered Jun 19 '13 at 19:46

In line:

senList[i] = string.join(item.split(' ').reverse(), ' ')

.reverse() reverse items in list object itself but returns nothing, so you can't use join in this way.

divide this line in two:

import string

def reverseSentences(text):
    senList = text.split('.')
    for i, item in enumerate(senList[:]):
        splited = item.split(' ')
        splited.reverse()
        senList[i] = string.join(splited, ' ')
    return string.join(senList, '.') + '.'

TypeError when using string.join() in Python

3 Answers3