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Why am I seeing "TypeError: string indices must be integers"?


Question

I'm playing with both learning python and trying to get github issues into a readable form. Using the advice on How can I convert JSON to CSV? I came up with this:

import json
import csv

f=open('issues.json')
data = json.load(f)
f.close()

f=open("issues.csv","wb+")
csv_file=csv.writer(f)

csv_file.writerow(["gravatar_id","position","number","votes","created_at","comments","body","title","updated_at","html_url","user","labels","state"])

for item in data:
        csv_file.writerow([item["gravatar_id"], item["position"], item["number"], item["votes"], item["created_at"], item["comments"], item["body"], item["title"], item["updated_at"], item["html_url"], item["user"], item["labels"], item["state"]])

Where "issues.json" is the json file containing my github issues. When I try to run that, I get

File "foo.py", line 14, in <module>
csv_file.writerow([item["gravatar_id"], item["position"], item["number"], item["votes"], item["created_at"], item["comments"], item["body"], item["title"], item["updated_at"], item["html_url"], item["user"], item["labels"], item["state"]])

TypeError: string indices must be integers

What am I missing here? Which are the "string indices"? I'm sure that once I get this working I'll have more issues, but for now , I'd just love for this to work!

When I tweak the for statement to simply

for item in data:
    print item

what I get is ... "issues" -- so I'm doing something more basic wrong. Here's a bit of my json:

{"issues":[{"gravatar_id":"44230311a3dcd684b6c5f81bf2ec9f60","position":2.0,"number":263,"votes":0,"created_at":"2010/09/17 16:06:50 -0700","comments":11,"body":"Add missing paging (Older>>) links...

when I print data it looks like it is getting munged really oddly:

{u'issues': [{u'body': u'Add missing paging (Older>>) lin...
2019/12/02
1
237
12/2/2019 3:53:35 PM

Accepted Answer

item is most likely a string in your code; the string indices are the ones in the square brackets, e.g., gravatar_id. So I'd first check your data variable to see what you received there; I guess that data is a list of strings (or at least a list containing at least one string) while it should be a list of dictionaries.

2011/05/20
125
5/20/2011 9:16:53 PM


data is a dict object. So, iterate over it like this:

Python 2

for key, value in data.iteritems():
    print key, value

Python 3

for key, value in data.items():
    print(key, value)
2017/10/03

TypeError for Slice Notation str[a:b]

tl;dr: use a colon : instead of a comma in between the two indices a and b in str[a:b]


When working with strings and slice notation (a common sequence operation), it can happen that a TypeError is raised, pointing out that the indices must be integers, even if they obviously are.

Example

>>> my_string = "hello world"
>>> my_string[0,5]
TypeError: string indices must be integers

We obviously passed two integers for the indices to the slice notation, right? So what is the problem here?

This error can be very frustrating - especially at the beginning of learning Python - because the error message is a little bit misleading.

Explanation

We implicitly passed a tuple of two integers (0 and 5) to the slice notation when we called my_string[0,5] because 0,5 (even without the parentheses) evaluates to the same tuple as (0,5) would do.

A comma , is actually enough for Python to evaluate something as a tuple:

>>> my_variable = 0,
>>> type(my_variable)
<class 'tuple'>

So what we did there, this time explicitly:

>>> my_string = "hello world"
>>> my_tuple = 0, 5
>>> my_string[my_tuple]
TypeError: string indices must be integers

Now, at least, the error message makes sense.

Solution

We need to replace the comma , with a colon : to separate the two integers correctly:

>>> my_string = "hello world"
>>> my_string[0:5]
'hello'

A clearer and more helpful error message could have been something like:

TypeError: string indices must be integers (not tuple)

A good error message shows the user directly what they did wrong and it would have been more obvious how to solve the problem.

[So the next time when you find yourself responsible for writing an error description message, think of this example and add the reason or other useful information to error message to let you and maybe other people understand what went wrong.]

Lessons learned

  • slice notation uses colons : to separate its indices (and step range, e.g. str[from:to:step])
  • tuples are defined by commas , (e.g. t = 1,)
  • add some information to error messages for users to understand what went wrong

Cheers and happy programming
winklerrr


[I know this question was already answered and this wasn't exactly the question the thread starter asked, but I came here because of the above problem which leads to the same error message. At least it took me quite some time to find that little typo.

So I hope that this will help someone else who stumbled upon the same error and saves them some time finding that tiny mistake.]

2019/04/26

I had a similar issue with Pandas, you need to use the iterrows() function to iterate through a Pandas dataset Pandas documentation for iterrows

data = pd.read_csv('foo.csv')
for index,item in data.iterrows():
    print('{} {}'.format(item["gravatar_id"], item["position"]))

note that you need to handle the index in the dataset that is also returned by the function.

2019/11/28

This can happen if a comma is missing. I ran into it when I had a list of two-tuples, each of which consisted of a string in the first position, and a list in the second. I erroneously omitted the comma after the first component of a tuple in one case, and the interpreter thought I was trying to index the first component.

2019/08/08