Error in writing Python dictionary to a file
Question
This is a simplified version of my code:
test={}
for i in range(10):
for j in range(15):
test[i,j]=i*j
with open('boo.json', 'w') as f:
json.dump(test, f)
and I got the following error:
raise TypeError("key " + repr(key) + " is not a string")
Any solution?
2 answers
solution1
2 ACCPTED 2015-06-30 17:51:48
The JSON format requires object keys to be strings; you cannot use tuples of numbers as keys.
You'll have to find a representation that uses strings instead that models your data well enough for you. You could use nested dictionaries and convert your numbers to strings, for example:
test = {}
for i in range(10):
nested = test[str(i)] = {}
for j in range(15):
nested[str(j)] = i * j
with open('boo.json', 'w') as f:
json.dump(test, f)
If you must have one level only, you'll have to produce a string with both integers in it; you could create a comma-separated key:
test['{},{}'.format(i, j)] = i * j
or use any other separator; you'll have to teach the JSON consumers to expect to parse those keys, of course.
Note that for your demo datastructure it'd be much easier to just use lists (JSON arrays); these are addressable with numbers after all:
test = []
for i in range(10):
nested = []
for j in range(15):
nested.append(i * j)
or using a list comprehension:
test = [[i * j for j in range(15)] for i in range(10)]
Demo:
>>> import json
>>> test = {}
>>> for i in range(10):
... nested = test[str(i)] = {}
... for j in range(15):
... nested[str(j)] = i * j
...
>>> print json.dumps(test, sort_keys=True, indent=4, separators=(',', ': '))
{
"0": {
"0": 0,
"1": 0,
"10": 0,
"11": 0,
"12": 0,
"13": 0,
"14": 0,
"2": 0,
"3": 0,
"4": 0,
"5": 0,
"6": 0,
"7": 0,
"8": 0,
"9": 0
},
"1": {
"0": 0,
"1": 1,
"10": 10,
"11": 11,
"12": 12,
"13": 13,
"14": 14,
"2": 2,
"3": 3,
"4": 4,
"5": 5,
"6": 6,
"7": 7,
"8": 8,
"9": 9
},
"2": {
"0": 0,
"1": 2,
"10": 20,
"11": 22,
"12": 24,
"13": 26,
"14": 28,
"2": 4,
"3": 6,
"4": 8,
"5": 10,
"6": 12,
"7": 14,
"8": 16,
"9": 18
},
"3": {
"0": 0,
"1": 3,
"10": 30,
"11": 33,
"12": 36,
"13": 39,
"14": 42,
"2": 6,
"3": 9,
"4": 12,
"5": 15,
"6": 18,
"7": 21,
"8": 24,
"9": 27
},
"4": {
"0": 0,
"1": 4,
"10": 40,
"11": 44,
"12": 48,
"13": 52,
"14": 56,
"2": 8,
"3": 12,
"4": 16,
"5": 20,
"6": 24,
"7": 28,
"8": 32,
"9": 36
},
"5": {
"0": 0,
"1": 5,
"10": 50,
"11": 55,
"12": 60,
"13": 65,
"14": 70,
"2": 10,
"3": 15,
"4": 20,
"5": 25,
"6": 30,
"7": 35,
"8": 40,
"9": 45
},
"6": {
"0": 0,
"1": 6,
"10": 60,
"11": 66,
"12": 72,
"13": 78,
"14": 84,
"2": 12,
"3": 18,
"4": 24,
"5": 30,
"6": 36,
"7": 42,
"8": 48,
"9": 54
},
"7": {
"0": 0,
"1": 7,
"10": 70,
"11": 77,
"12": 84,
"13": 91,
"14": 98,
"2": 14,
"3": 21,
"4": 28,
"5": 35,
"6": 42,
"7": 49,
"8": 56,
"9": 63
},
"8": {
"0": 0,
"1": 8,
"10": 80,
"11": 88,
"12": 96,
"13": 104,
"14": 112,
"2": 16,
"3": 24,
"4": 32,
"5": 40,
"6": 48,
"7": 56,
"8": 64,
"9": 72
},
"9": {
"0": 0,
"1": 9,
"10": 90,
"11": 99,
"12": 108,
"13": 117,
"14": 126,
"2": 18,
"3": 27,
"4": 36,
"5": 45,
"6": 54,
"7": 63,
"8": 72,
"9": 81
}
}
or producing a flat structure:
>>> test = {}
>>> for i in range(10):
... for j in range(15):
... test['{},{}'.format(i, j)] = i * j
...
>>> print json.dumps(test, sort_keys=True, indent=4, separators=(',', ': '))
{
"0,0": 0,
"0,1": 0,
"0,10": 0,
"0,11": 0,
"0,12": 0,
"0,13": 0,
"0,14": 0,
"0,2": 0,
"0,3": 0,
"0,4": 0,
"0,5": 0,
"0,6": 0,
"0,7": 0,
"0,8": 0,
"0,9": 0,
"1,0": 0,
"1,1": 1,
"1,10": 10,
"1,11": 11,
"1,12": 12,
"1,13": 13,
"1,14": 14,
"1,2": 2,
"1,3": 3,
"1,4": 4,
"1,5": 5,
"1,6": 6,
"1,7": 7,
"1,8": 8,
"1,9": 9,
"2,0": 0,
"2,1": 2,
"2,10": 20,
"2,11": 22,
"2,12": 24,
"2,13": 26,
"2,14": 28,
"2,2": 4,
"2,3": 6,
"2,4": 8,
"2,5": 10,
"2,6": 12,
"2,7": 14,
"2,8": 16,
"2,9": 18,
"3,0": 0,
"3,1": 3,
"3,10": 30,
"3,11": 33,
"3,12": 36,
"3,13": 39,
"3,14": 42,
"3,2": 6,
"3,3": 9,
"3,4": 12,
"3,5": 15,
"3,6": 18,
"3,7": 21,
"3,8": 24,
"3,9": 27,
"4,0": 0,
"4,1": 4,
"4,10": 40,
"4,11": 44,
"4,12": 48,
"4,13": 52,
"4,14": 56,
"4,2": 8,
"4,3": 12,
"4,4": 16,
"4,5": 20,
"4,6": 24,
"4,7": 28,
"4,8": 32,
"4,9": 36,
"5,0": 0,
"5,1": 5,
"5,10": 50,
"5,11": 55,
"5,12": 60,
"5,13": 65,
"5,14": 70,
"5,2": 10,
"5,3": 15,
"5,4": 20,
"5,5": 25,
"5,6": 30,
"5,7": 35,
"5,8": 40,
"5,9": 45,
"6,0": 0,
"6,1": 6,
"6,10": 60,
"6,11": 66,
"6,12": 72,
"6,13": 78,
"6,14": 84,
"6,2": 12,
"6,3": 18,
"6,4": 24,
"6,5": 30,
"6,6": 36,
"6,7": 42,
"6,8": 48,
"6,9": 54,
"7,0": 0,
"7,1": 7,
"7,10": 70,
"7,11": 77,
"7,12": 84,
"7,13": 91,
"7,14": 98,
"7,2": 14,
"7,3": 21,
"7,4": 28,
"7,5": 35,
"7,6": 42,
"7,7": 49,
"7,8": 56,
"7,9": 63,
"8,0": 0,
"8,1": 8,
"8,10": 80,
"8,11": 88,
"8,12": 96,
"8,13": 104,
"8,14": 112,
"8,2": 16,
"8,3": 24,
"8,4": 32,
"8,5": 40,
"8,6": 48,
"8,7": 56,
"8,8": 64,
"8,9": 72,
"9,0": 0,
"9,1": 9,
"9,10": 90,
"9,11": 99,
"9,12": 108,
"9,13": 117,
"9,14": 126,
"9,2": 18,
"9,3": 27,
"9,4": 36,
"9,5": 45,
"9,6": 54,
"9,7": 63,
"9,8": 72,
"9,9": 81
}
solution2
1 2015-06-30 17:52:50
You need your json object keys to be strings.
Try doing this instead:
#!/usr/bin/env python3
import json
test={}
for i in range(10):
for j in range(15):
test["%s,%s" %(i,j)]=i*j
with open('boo.json', 'w') as f:
json.dump(test, f)
This will put the values for i and j into string format ( with a comma in between) so your key will be a string.
@Martijn does a better job explaining in his answer.
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