Flask custom error handling for upload function

I have developed an upload form to take specific .xlsx file as upload. The requirement is to handle any exceptions for upload of non xlsx (for e.g. zip, exe file). I am using pyexcel library for reading the upload. I tried creating following code to handle this exception:

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The error handling code is as follows:

class FILE_TYPE_NOT_SUPPORTED_FMT(Exception):
pass

@app.errorhandler(FILE_TYPE_NOT_SUPPORTED_FMT)
def custom_handler(errrors):
app.logger.error('Unhandled Exception: %s', (errrors))
return render_template('400.html'), 400

and the upload code is as follows:

@users.route("/oisdate_upload", methods=['GET', 'POST'])
@login_required
def doimport_ois_date():
msg=None
if request.method == 'POST':

def OIS_date_init_func(row):
#c.id = row['id']
c = Ois_date(row['date'],row['on'],row['m1'],row['m2'],row['m3'],row['m6'],row['m9'],row['y1'],row['y2'],row['y3'],row['y4'],row['y5'],row['y7'],row['y10'])
return c

request.save_book_to_database(
field_name='file', session=db.session,
tables=[Ois_date],
initializers=[OIS_date_init_func])
msg = "Successfully uploaded"
#return redirect(url_for('users.doimport_ois_date'), code=302)
if((Ois_date.query.order_by(Ois_date.date.desc()).first()) is not None):
date_query = Ois_date.query.order_by(Ois_date.date.desc()).first()
start_date = date_query.date
date_query1 = Ois_date.query.order_by(Ois_date.date.asc()).first()
end_date = date_query1.date

return render_template('OISdate_upload.html',msg=msg, start_date=start_date,end_date=end_date)

I am unable to figure out how to correctly capture the error and handle it, any feedback would be appreciated.

Solution

You have two options to handle this exception.

1) you import the exception directly from the pyexcel package and use it as the error:

e.g.

from pyexcel.exceptions import FileTypeNotSupported
...
@app.errorhandler(FileTypeNotSupported)
...

2) Or, you can wrap the code where you want to load the spreadsheet in a try-except block and throw a custom error.

from pyexcel.exceptions import FileTypeNotSupported

class CustomError(Exception)
    pass

@app.errorhandler(CustomError)
    # do something
    pass

@app.route('/upload_excel')
def upload_excel():
    try:
        function_where_you_load_excel()
    except FileTypeNotSupported:
        raise CustomError