Python: how to load json with dict containing range

Question

my python code is about generating a sequence number from a dict keys, and my dict keys are defined with a range using cycle package in itertools module.

working example:

from itertools import cycle

e = {'Apple': cycle(range(1,999)),'Orange': cycle(range(1,999)),'Banana': cycle(range(1,999))}

def SequenceNum(f):
    return f'{next(e[f])}'.zfill(3)

X = SequenceNum('Apple')
print(X)

output

001 --> it keeps incrementing in the range specified above in dict `e`

Challenge:

My requirement is to convert this dict of e into a json file. So it will load keys and values by parsing json file.

cat test.json

{
    "DATA": {
        "Apple": "cycle(range(1,999))",
        "Orange": "cycle(range(1,999))",
        "Banana": "cycle(range(1,999))"
    }
}

(i had to put the dict values inside double quotes to avoid json file loading error.)

code

import json
from itertools import cycle

with open('test.json') as f:
    FromJson = json.load(f)
d = FromJson['DATA']
print(d)

def SequenceNum(f):
    return f'{next(d[f])}'.zfill(3)

X = SequenceNum('Apple')
i = 1
while i <= 10:
    print(i, SequenceNum('Apple'))
    i += 1

here new dict is d that loads json file and it will load the values in single quotes.

output

{'Apple': 'cycle(range(1,999))', 'Orange': 'cycle(range(1,999))', 'Banana': 'cycle(range(1,999))'} #THIS IS OUTPUT of 'd' after loading json file

Traceback (most recent call last):
  File "c:\Users\chandu\Documents\test.py", line 14, in <module>
    print(i, SequenceNum('Apple'))
  File "c:\Users\chandu\Documents\test.py", line 12, in SequenceNum
    return f'{next(d[f])}'.zfill(3)
TypeError: 'str' object is not an iterator

it is giving error because my dict values are not properly iterable by cycle itertools modules, since they are in quotes. i dont know if there is any other cause for this error.

please help to resolve this error,

Thanks in advance.

Answer 1

If you are sure what each value is, you can do eval with care:

def SequenceNum(f):
    return f'{next(eval(d[f]))}'.zfill(3)

Note this is very dangerous to use, because eval evaluates anything that is passed into it and can cause harm.

---

This also will always fetch first value from iterator as it is evaluated new everytime. To solve, you can:

def SequenceNum(f):
    return eval(d[f])

i = 1
seq_iter = SequenceNum('Apple')
while i <= 10:
    print(i, f'{next(seq_iter)}'.zfill(3))
    i += 1