Unable to concatenate fields in ArcGIS Pro

Description

The Calculate Field tool in ArcGIS Pro allows concatenating fields, to merge or summarize two or more attributes into one field. In some instances, the process fails with the 000539 error message. Below are examples of other error messages that may be returned pertaining to the same problem:

Error:   
exceptions.TypeError: cannot concatenate 'str' and 'int' objects

Error:   
TypeError: unsupported operand type(s) for +: 'float' and 'str'

Cause

The error message is returned when attempting to concatenate different types of fields into a field.

Solution or Workaround

To resolve this issue, ensure the fields are of the same type before concatenating. For example, concatenate a string field with another string field, or integer field with an integer field. If the fields are of different types, identify the field types and change them to fit only one type.

To change the field data type from string to numeric, refer to How To: Convert a string field to a numeric field. To change a numeric field to a string field, refer to How To: Convert a number field to a string field.

Note:
Transferring attributes from a text field to a field with numeric data type requires only numbers as attributes, and no other characters except for decimal points. Changing data types may also lead to loss of data. For example, changing a long integer or float to a short integer, or a blob to a text.