python - ValueError: dict contains fields not in fieldnames

38
votes

Can someone help me with this.

I have my Select query

selectAttendance = """SELECT * FROM table """

And I want the content of my select query and include a header when I download the csv file, So I did this query:

with open(os.path.join(current_app.config['UPLOAD_FOLDER'], 'csv.csv'), 'wb') as csvfile:
                writer = csv.DictWriter(csvfile,fieldnames  = ["Bio_Id","Last_Name","First_Name","late","undertime","total_minutes", "total_ot", "total_nsd", "total_absences"], delimiter = ';')
                writer.writeheader()
                writer.writerow(db.session.execute(selectAttendance))
            db.session.commit()

but it gives me this error

**ValueError: dict contains fields not in fieldnames**

I want to have like this output in my downloaded csv file:

Bio_Id Last_Name First_Name late undertime total_minutes total_ot total_nsd total_absences
1      Joe       Spark       1     1            2            1        1          1

Thank you in advance.

3
pythoncsv
So have you looked at the dictionary and compared it to the headers you specify? - jonrsharpe
What's unclear in the error message? - BartoszKP
I don't know why after ValueError: dict contains fields not in fieldnames:***content of the select*** not saving in the specified csv - akbsmile
Because after the error nothing happens; the program has crashed. - jonrsharpe
@BartoszKP Im here cuz I dont understand the error msg, can you explain it? - Charlie Parker

3 Answers

19
votes

As the error states: the dictionary that comes from the query contains more key than the field names you specified in the DictWriter constructor.

One solution would be to filter that in advance, something like this:

field_names = ["Bio_Id","Last_Name", ...]
writer = csv.DictWriter(csvfile,fieldnames=field_names , delimiter = ';')
writer.writeheader()
data = {key: value for key, value in db.session.execute(selectAttendance).items()
        if key in field_names}
writer.writerow(data)

Another solution could be to construct the query using only those fields:

query = 'SELECT %s FROM table' % ', '.join(field_names)

However, Tim Pietzcker's answer is the best.

150
votes

As the error message clearly states, your dictionary contains keys that don't have a corresponding entry in your fieldnames parameter. Assuming that these are just extra fields, you can ignore them by using the extrasaction parameter during construction of your DictWriter object:

writer = csv.DictWriter(csvfile, fieldnames=["Bio_Id","Last_Name","First_Name","late","undertime","total_minutes", "total_ot", "total_nsd", "total_absences"], 
                        extrasaction='ignore', delimiter = ';')
-2
votes

Hi all thank you for answering. I finally found out how to make it. here is the code

    w = csv.writer(file(r'test.csv','wb'), delimiter=';')
    w.writerows([["Bio Id","Last Name",.....]])
    w.writerows(db.session.execute(selectAttendance))
    db.session.commit()