python - Name is not defined in a list comprehension with multiple loops -


i'm trying unpack complex dictionary , i'm getting nameerror in list comprehension expression using multiple loops:

a={   1: [{'n': 1}, {'n': 2}],   2: [{'n': 3}, {'n': 4}],   3: [{'n': 5}], } = [1,2] print [r['n'] r in a[g] g in good] # nameerror: name 'g' not defined

you have order of loops mixed up; considered nested left right, for r in a[g] outer loop , executed first. swap out loops:

print [r['n'] g in r in a[g]]

now g defined next loop, for r in a[g], , expression no longer raises exception:

>>> a={ ...   1: [{'n': 1}, {'n': 2}], ...   2: [{'n': 3}, {'n': 4}], ...   3: [{'n': 5}], ... } >>> = [1,2] >>> [r['n'] g in r in a[g]] [1, 2, 3, 4]

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