[ARROW-6158] [Python] possible to create StructArray with type that conflicts with child array's types

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.15.0
• Component/s: Python
• Labels: pull-request-available
• External issue URL: https://github.com/apache/arrow/issues/22551
• Assignee: Joris Van den Bossche
• Reporter: Joris Van den Bossche
• Created: 07/Aug/19 10:58
• Updated: 11/Jan/23 07:45
• Resolved: 25/Sep/19 03:05

Description

Using the Python interface as example. This creates a StructArray where the field types don't match the child array types:

a = pa.array([1, 2, 3], type=pa.int64())
b = pa.array(['a', 'b', 'c'], type=pa.string())
inconsistent_fields = [pa.field('a', pa.int32()), pa.field('b', pa.float64())]

a = pa.StructArray.from_arrays([a, b], fields=inconsistent_fields) 

The above works fine. I didn't find anything that errors (eg conversion to pandas, slicing), also validation passes, but the type actually has the inconsistent child types:

In [2]: a
Out[2]: 
<pyarrow.lib.StructArray object at 0x7f450af52eb8>
-- is_valid: all not null
-- child 0 type: int64
  [
    1,
    2,
    3
  ]
-- child 1 type: string
  [
    "a",
    "b",
    "c"
  ]

In [3]: a.type
Out[3]: StructType(struct<a: int32, b: double>)

In [4]: a.to_pandas()
Out[4]: 
array([{'a': 1, 'b': 'a'}, {'a': 2, 'b': 'b'}, {'a': 3, 'b': 'c'}],
      dtype=object)

In [5]: a.validate() 

Shouldn't this be disallowed somehow? (it could be checked in the Python from_arrays method, but maybe also in StructArray::Make which already checks for the number of fields vs arrays and a consistent array length).

Similarly to discussion in ARROW-6132, I would also expect that this the ValidateArray catches this.

Issue Links

• links to: GitHub Pull Request #5488