5

So I am extracting data from a JSON file.

I am trying to pack my data in a way so a preprocessing script can use it.

preprocessing script code:

for key in split:
    hist = split[key]
    for text, ans, qid in hist:

Now I have an extracted dataset into a Dictionary like this:

dic{}
result //is the result of removing some formatting elements and stuff from the Question, so is a question string
answer //is the answer for the Q
i // is the counter for Q & A pairs

So I have

this = (result,answer,i)
dic[this]=this

And when I try to replicate the original code I get the Too many values to unpack error

for key in dic:
    print(key)
    hist = dic[key]
    print(hist[0])
    print(hist[1])
    print(hist[2])
    for text, ans, qid in hist[0:2]:  // EDIT: changing this to hist[0:3] or hist has no effect
        print(text)

OUTPUT:

(u'This type of year happens once every four', u'leap', 1175)
This type of year happens once every four
leap
1175
Traceback (most recent call last):
  File "pickler.py", line 34, in <module>
    for text, ans, qid in hist[0:2]:
ValueError: too many values to unpack

As you can see I even tried limiting the right side of the assignment but that didn't help either

and as you can see the output matches as it should for each item

hist[0]=This type of year happens once every four
hist[1]=leap
hist[2]=1175

And len(hist) returns 3 also.

Why the hell is this happening? Having hist,hist[:3],hist[0:3] has the same result, Too many values to unpack error.

KameeCoding
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    Can you please correct the indentation levels of your example code, so we can see the code blocks? Thanks! – Klaus D. Jan 21 '15 at 15:16

3 Answers3

13

What you want is 

text, ans, qid = hist
print(text)

instead of 

for text, ans, qid in hist:

Think about what hist represents - it is a single tuple (because you've looked it up with key)

That means that

for text, ans, qid in hist:

is trying to iterate through each member of the tuple and break them into those three components. So, first, it tries to act on hist[0] i.e. "This type of year...." and tries to break it into text, ans and qid. Python recognises that the string could be broken up (into characters), but can't work out how to break it into those three components as there are far more characters. So it throws the Error 'Too many values to unpack'

J Richard Snape
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2

What your loop is trying to do is iterate through the first three items of hist and interpret EACH of them individually as a three-element tuple. I'd guess what you are trying to do is this:

for key in dic:
    hist = dic[key]
    (text, ans, qid) = hist[0:3] # Might not need this slice notation if you are sure of the number of elements
    print(text)
rchang
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  • @Kameegaming I tried to replicate as much of your situation as I could here: http://repl.it/8aC (click "run session"). Did I overlook something? – rchang Jan 21 '15 at 15:44
  • seems correct, this one actually works, even if I leave [0:3] out, but doesn't work with for, which is weird, huh – KameeCoding Jan 21 '15 at 15:49
  • Good answer. See my slightly longer one for an explanation why it doesn't work with `for` – J Richard Snape Jan 21 '15 at 15:52
2

change this:

for text, ans, qid in hist[0:2]:

to this:

for text, ans, qid in hist[0:3]:

hist[x:y] is all the elements from hist with x <= ids < y

EDIT:

As pointed out by @J Richard Snape and @rchang you can't use this:

for text, ans, qid in hist[0:3]:

but you can use this instead (worked for me):

for text, ans, qid in [hist[0:3]]:
JasonPap
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