Key Error when defining string, python

Question

I get the error "Key error:'name' "

Can anyone tell what the problem is with the following code:

import random

def mongoCountry(countryNum, provinceNum):
    """generate some test data"""
    f = open("F:\\univData\\country-mongo.json", mode = 'w')
    text = ""
    for c_n in range(0, countryNum):
        for p_n in range(0, provinceNum):
            text += "{name:country{0},provinces:[{$ref : Province,$id :   province{1}}]}\n".format(c_n, p_n)
    f.write(text)
    f.close()

mongoCountry(2, 10)

I googled it so I know it's about dict() object. but I can't find any such object there.

will you please give detail error ?

NPatel
– NPatel

2014-07-04 03:43:33 +00:00
Commented Jul 4, 2014 at 3:43 — NPatel
– NPatel, Commented Jul 4, 2014 at 3:43

thefourtheye · Accepted Answer · 2014-07-04 04:46:29Z

1

If I understand your program correctly, you are trying to create a JSON object. As iCodez said in his answer, Python's format function treats the entire string as the format string (or template string, if you like). To override that, you can escape the format strings like this

"{{name:country{0},provinces:[{{$ref : Province,$id : province{1}}}]}}\n".format(c_n, p_n)

You will get something like the following if c_n and p_n are "Welcome" and "123"

{name:countryWelcome,provinces:[{$ref : Province,$id :   province123}]}

answered Jul 4, 2014 at 4:46

thefourtheye

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NPatel · Accepted Answer · 2014-07-04 03:50:39Z

1

You are starting your string with {name: so format need name as a key.

Please escape { before name.

https://docs.python.org/2/library/string.html#format-examples

answered Jul 4, 2014 at 3:50

NPatel

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score 1 · Accepted Answer · 2014-07-04 03:55:57Z

1

str.format is treating the entire string as a format field because it begins with {name: and ends with }. Below is a demonstration with a simpler string:

>>> '{a:{0}}'.format(1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 'a'
>>>

To fix the problem, you can use the old % formatting:

text += "{name:country%i,provinces:[{$ref : Province,$id :   province%i}]}\n" % (c_n, p_n)

edited Jul 4, 2014 at 3:55

answered Jul 4, 2014 at 3:50

user2555451

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