Aggregate is broken when supplying single key in an array

Minimal, reproducible code sample, a copy-pastable example if possible

import petl

table1 = [['foo', 'bar'],
          ['aaa', 1],
          ['aaa', 2],
          ['bbb', 3],
          ['bbb', 4],
          ['bbb', 5],
          ['ccc', 6]]


table2 = petl.aggregate(table1, key=["foo", ], aggregation=len)

print(table2)
"""
+-----+-------+---+---+
| foo | value |   |   |
+=====+=======+===+===+
| a   | a     | a | 2 |
+-----+-------+---+---+
| b   | b     | b | 3 |
+-----+-------+---+---+
| c   | c     | c | 1 |
+-----+-------+---+---+
"""

Problem description

Seems that iteration is broken somewhere inside aggregation when a key is supplied as a single element of a list. Happened upon it while using key programmatically and the user supplied a single value.

At the very least, should error/fail instead of acting this unpredictably.

Thanks for looking into it 😃

Version and installation information

• petl.__version__ == 1.7.4
• Python 3.8.5 (default, Jan 27 2021, 15:41:15) [GCC 9.3.0] on linux
• Installed via pip into virtual environment

[juarezr]

@MalayGoel, thanks.

[juarezr]

Hi @MalayGoel,

Would you mind sending a PR?