Python when catching exceptions, how I can get the line number?

Question

I know there is another thread on this but it didn't solve my problem, please read my question!

Basically, I'm parsing a YAML file to ensure it has all the correct keys and values I want. If the YAML file has an incorrect value or key that it needs to have, then I want to print a message that says where the incorrect value or key is.

Example:
Let's say for this YAML file:

Groceries:
Apples: Granny
Milk: Skim
Bread: Wheat

Let's say I was expecting 'Whole' as the value for 'Milk'. If that line is line 3, how do I print a message that says "error: invalid value blah blah on LINE 3"??

Thanks so much!

read the file line by line and print the counter for your current line number when you get an error? — normalppl
– normalppl, Commented Jun 20, 2011 at 21:26
I'm sorry I'm fairly new to Python and programming in general. Can you give me an example? are you saying create said counter or one already exists? — Ken
– Ken, Commented Jun 20, 2011 at 21:28
don't know how u parse your file. but if you just uses some external library and get an exception you can use traceback.tb_lineno. docs.python.org/library/traceback.html — normalppl
– normalppl, Commented Jun 20, 2011 at 21:34
Depends heavily on how you parse the file. I fear that most ready-made parsing libraries won't pass line numbers on - so if you can only detect the error after that libary finished parsing and returned a complete Python object, you're propably out of luck. — user395760
– user395760, Commented Jun 20, 2011 at 21:37
How do you parse the YAML? Do you use a library like PyYAML? Or do you use a different aproach? — codeape
– codeape, Commented Jun 20, 2011 at 21:39

Jakob Bowyer · Accepted Answer · 2011-06-20 21:40:02Z

5

From the PyYaml documentation

>>> try:
...     yaml.load("unbalanced blackets: ][")
... except yaml.YAMLError, exc:
...     if hasattr(exc, 'problem_mark'):
...         mark = exc.problem_mark
...         print "Error position: (%s:%s)" % (mark.line+1, mark.column+1)

Error position: (1:22)

answered Jun 20, 2011 at 21:40

Jakob Bowyer

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3 Comments

Kobi K Over a year ago

I know it's a bit old but but i think mark.line+1 needs to be just mark.line.

hdgarrood Over a year ago

I don't think this answers the question - the asker is concerned about data validation, not syntax validation. The example is valid YAML, so loading it won't throw a YAMLError.

Ray Salemi Over a year ago

Without the +1 the line and column numbers seem to start at 0.

Michael Barton · Accepted Answer · 2014-08-15 17:40:35Z

0

I had a similar requirement to the question. I couldn't find a python solution but found kwalify - http://www.kuwata-lab.com/kwalify. You can use it as a command line tool. It allows you to specify the keys, and allowable values as a schema. You then validate your YAML file as follows:

kwalify -f schema.yaml document.yaml

answered Aug 15, 2014 at 17:40

Michael Barton

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