CODEWITHSUNDEEP
pythonpsycopg2
Timothy Grant
Timothy Grant

Reputation: 141

Python thinks that psycopg2 DictRow is list (At least that's what it looks like)

I have some code that originally looked like this (it's part of a for loop that iterates through the results of a query):

title['name'] += 'x'

I sometimes get the following exception (always on the same row):

<class 'psycopg2.extras.DictRow'>
Traceback (most recent call last):
  File "rtk_film_nos.py", line 231, in <module>
    main()
  File "rtk_film_nos.py", line 150, in main
    title['name'] += 'x'
TypeError: list indices must be integers, not str

I changed the code to be more verbose:

foo = title['name']
foo += 'x'
print type(title)
title['name'] = foo

The exception changed to:

<class 'psycopg2.extras.DictRow'>
Traceback (most recent call last):
  File "rtk_film_nos.py", line 231, in <module>
    main()
  File "rtk_film_nos.py", line 150, in main
    title['name'] = foo
TypeError: list indices must be integers, not str

If I wrap the code in a try/except it will quite happily print the contents of title['name'].

I'm at a loss as to what I'm doing wrong. It seems that for some reason python (v2.6.6) is deciding to treat the dict as a list but I have no idea why.

Upvotes: 1

Views: 1877

Answers (1)

Martijn Pieters
Martijn Pieters

Reputation: 1124188

The DictRow class is a subclass of list, and until version 2.3.0 you could not use it to assign to elements by name.

You can work around this by looking up the column index directly:

title[title._index['name']] = foo

or, for your augmented assignment:

title[title._index['name']] += 'x'

Upvotes: 3

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