Python only using first letter in string when searching keys in a dictionary

Question

Python beginner here. I am having a problem when attempting to search for a string within a dictionary.

The program I am writing is using xlrd to match data from a excel spreadsheet (S2name) with a dictionary key, to then return the value assigned to the key. This is for the purpose of matching quality control tests with chemical data.

The dictionary is much like this:

dQC = {'4266152-001': 'METHOD_BLANK',
 '4266152-002': 'LCS',
 '4266152-004': 'LAB_DUPLICATE',

etc..

My code is working, except for the fact that the search function is returning the wrong result from the dictionary.

I have isolated the problem to the v variable in the following:

S2name = (sheet2.cell_value(row_index, 0))

for key, value in dQC.items(): 
    def search(dic, lookup):   
        for v in key:  
            print("This should be the key in dQC, not the number %s" % v)
            if v in lookup:    
                return v   # I would obviously return value here, but it returns the wrong one.
            else:
                return False

QCtype = (search(dQC, S2name))

print(QCtype)

Result:

This should be the key in dQC, not the number 4
4

For some reason, v is searching for only the first digit in the string (ie: 4) and not the whole string (ie: 4266152-001), so when I call the value using QCtype, it returns the wrong one. I would like v to use the first 10 characters when iterating the search, not he first.

Note, in the script, I am returning v just to check it. I would otherwise be returning value.

EDIT:

Perhaps it is clearer if I link to the thread that I used some of the code from.

I was under the assumption that this would search for the entire word in the dictionary key, not for the individual letters in key, which makes sense to me now.

How to search if dictionary value contains certain string with Python

Why are you iterating over the key at all? The key is just one string; just use it directly. — BrenBarn, Jan 06 '15 at 04:30
Why are you defining the search function inside the for loop? — PM 2Ring, Jan 06 '15 at 04:35
in you code v is a character in the string key. `search` function returns that character when `lookup` has the character also. it does not return the wrong one. — salmanwahed, Jan 06 '15 at 04:36

score 4 · Answer 1 · answered Jan 06 '15 at 04:35

You're defining many functions named search, each obliterating the other, and at the end only calling the last one you happened to have defined. It's unusual to use the def statement in a loop, and surely wrong to use def but not call/use that function within each leg of the loop.

Moreover, for v in key:, where key is a string, assigns to v, in succession, each of the characters in key.

It's hard to fathom exactly what you think you're doing, but I imagine you'd want to define search just once and then maybe call it in a loop. Perhaps something like:

def search(dic, lookup, valur):   
    return lookup.get(key, value)

for key, value in dQC.items():
    QCtype = search(dQC, S2name)
    print(QCtype)

...?

Python only using first letter in string when searching keys in a dictionary

1 Answers1