topic Re: UpdateCursor - sequence size? in Python Questions

UpdateCursor - sequence size?

BenLeslie1 — Wed, 29 Oct 2014 15:32:16 GMT

I'm trying to use UpdateCursor to insert some text into an attribute. The attribute is a text field ten characters in length. However the script will only work for values of one character in length.

i.e. if MyValue = "A" the script works

but if MyValue = "All" the error says 'sequence size must match size of the row'

with arcpy.da.UpdateCursor(MyFeatureLyr, MyAttribute) as cursor:
     for row in cursor:
          cursor.updateRow(MyValue)

Re: UpdateCursor - sequence size?

DallasShearer — Wed, 29 Oct 2014 20:59:21 GMT

the updateRow needs to be sent a tupple even if it's only one variable being sent.

change the updaterow to this and it should work

cursor.updateRow((MyValue,))

Re: UpdateCursor - sequence size?

DanPatterson_Retired — Wed, 29 Oct 2014 21:37:27 GMT

The help files says lists or tuples can be used for parameters that require them, see da.UpdateCursor help if so, I would do it explicitly using the list and tuple methods

>>> a= list('astring')

>>> a

['a', 's', 't', 'r', 'i', 'n', 'g']

>>> b = tuple('astring')

>>> b

('a', 's', 't', 'r', 'i', 'n', 'g')

>>>

or in your case list(MyValue) or tuple(MyValue) in the appropriate line(s)

Re: UpdateCursor - sequence size?

JoshuaBixby — Thu, 30 Oct 2014 01:20:24 GMT

I don't think using the list or tuple function in the way described here will yield the desired result. In the original code snippet, I understand MyAttribute to be a single field/attribute, and that the goal is to populate that attribute with "ALL" or some other multi-character string. Since a multi-character string is iterable, passing MyValue to the tuple function will result in a tuple with multiple single-character items instead of a tuple with a single multi-character items, as demonstrated.

The suggestion by Dallas Shearer‌ works since it passes the update cursor a single item multi-character tuple, which is what I think the OP is after.

Re: UpdateCursor - sequence size?

DanPatterson_Retired — Thu, 30 Oct 2014 10:28:47 GMT

I agree...I guess my point wasn't clear...sorry...
Manually create the tuple from a string, requires entering the , directly

>>> a = ("astring",) # create the tuple directly

>>> a

('astring',)

If you have a list of string already

>>> a = ["astring"]

>>> b = tuple(a)

>>> b

('astring',)

>>>

If you just have a string, in either case of the tuple or list, you still have to add the string to it otherwise the string is treated as the iterable