How to skip over any value that is not in a range in a for loop

Question

I am trying to create 3 nested for loops and skip over any values that is not in any of the for loops. I have tried different ways but have not had much success yet. Here is the for loops:

for industry in string.ascii_uppercase:
    for code in range(1, 99):
        for year in range(1998, 2019):
            createCSV(industry, code, year)

the problem is there are industry and code values for which data is not available. The code breaks at code=3 because 3 is missing in the original values for the variable code. If it was only one value I could just skip it using continue.

for industry in string.ascii_uppercase:
for code in range(1, 99):
    if code == 3:
        continue
    for year in range(1998, 2019):
        createCSV(industry, code, year)

But there more missing values for both industry and code and I am trying to find an efficient way. Thanks for your help.

Sounds like you clearly know what values are invalid so why not just store them in a `set` and then check containment while looping? — pstatix, Jan 01 '19 at 20:12
@pstatix and Carciagenicate I do not know what values are missing but I can figure that out. however, it would take time and the missing list would be too long so i am looking for a more efficient way to do that. — josh, Jan 01 '19 at 21:19

Xukrao · Accepted Answer · 2019-01-01T20:34:28.010

One possible way could be with a try/except clause:

for industry in string.ascii_uppercase:
    for code in range(1, 99):
        for year in range(1998, 2019):
            try:
                createCSV(industry, code, year)
            except Exception:
                print(f"Warning: unable to create CSV for industry '{industry}' for code '{code}' for year '{year}'")

in which you can still replace the generic Exception with the specific exception class that your createCSV function raises. If you know for example that createCSV will raise a ValueError when an invalid code value is provided as input argument, then replace except Exception: with except ValueError:. This will help avoid some potential pitfalls (see here for more info).

However if at all possible I would recommend to instead:

Retrieve an iterable with only the valid codevalues beforehand and then only loop over these, OR
Modify the programming code of createCSV such that it doesn't break when an invalid code value is provided.

Bitto · Answer 2 · 2019-01-01T20:30:20.863

If you already know which values causes error then avoid looping over them.

missing_code_values=[3,4,5,6,7,83]
missing_ascii_values=['A','Z']
for industry in [x for x in string.ascii_uppercase if x not in missing_ascii_values]:
    for code in [x for x in range(1, 99) if x not in missing_code_values]:
        for year in range(1998, 2019):
            createCSV(industry, code, year)

If you don't know it, then you can use try/except

for industry in string.ascii_uppercase:
    for code in range(1, 99):
        for year in range(1998, 2019):
            try:
                createCSV(industry, code, year)
            except: # mention specific exception if you can
                print("Skipping Industry-",industry," Code-",code," Year-",year)

score -3 · Answer 3 · answered Jan 01 '19 at 20:11

-3

You can check against Null in Python:

 for industry in string.ascii_uppercase:
 for code in range(1, 99):
   if code is None:
     continue
 for year in range(1998, 2019):
   createCSV(industry, code, year)

answered Jan 01 '19 at 20:11

Janneck Lange

882
2
11
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This won't work because `code` wont be `None` when iterating the range. The OP is stating that they know which values they need to skip, not test for nullness. – pstatix Jan 01 '19 at 20:13

How to skip over any value that is not in a range in a for loop

3 Answers3