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Commit94aceed

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Support multi-dimensional arrays in PL/python.
Multi-dimensional arrays can now be used as arguments to a PL/python function(used to throw an error), and they can be returned as nested Python lists.This makes a backwards-incompatible change to the handling of compositetypes in arrays. Previously, you could return an array of composite typesas "[[col1, col2], [col1, col2]]", but now that is interpreted as a two-dimensional array. Composite types in arrays must now be returned asPython tuples, not lists, to resolve the ambiguity. I.e. "[(col1, col2),(col1, col2)]".To avoid breaking backwards-compatibility, when not necessary, () is stillaccepted for arrays at the top-level, but it is always treated as asingle-dimensional array. Likewise, [] is still accepted for composite types,when they are not in an array. Update the documentation to recommend using []for arrays, and () for composite types, with a mention that those other thingsare also accepted in some contexts.This needs to be mentioned in the release notes.Alexey Grishchenko, Dave Cramer and me. Reviewed by Pavel Stehule.Discussion: <CAH38_tmbqwaUyKs9yagyRra=SMaT45FPBxk1pmTYcM0TyXGG7Q@mail.gmail.com>
1 parent8c035e5 commit94aceed

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‎doc/src/sgml/plpython.sgml‎

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Original file line numberDiff line numberDiff line change
@@ -451,13 +451,13 @@ $$ LANGUAGE plpythonu;
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<para>
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SQL array values are passed into PL/Python as a Python list. To
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return an SQL array value out of a PL/Python function, return a
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Pythonsequence, for example alist or tuple:
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Python list:
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<programlisting>
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CREATE FUNCTION return_arr()
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RETURNS int[]
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AS $$
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return(1, 2, 3, 4, 5)
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return[1, 2, 3, 4, 5]
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$$ LANGUAGE plpythonu;
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SELECT return_arr();
@@ -467,6 +467,34 @@ SELECT return_arr();
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(1 row)
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</programlisting>
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Multidimensional arrays are passed into PL/Python as nested Python lists.
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A 2-dimensional array is a list of lists, for example. When returning
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a multi-dimensional SQL array out of a PL/Python function, the inner
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lists at each level must all be of the same size. For example:
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<programlisting>
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CREATE FUNCTION test_type_conversion_array_int4(x int4[]) RETURNS int4[] AS $$
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plpy.info(x, type(x))
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return x
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$$ LANGUAGE plpythonu;
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SELECT * FROM test_type_conversion_array_int4(ARRAY[[1,2,3],[4,5,6]]);
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INFO: ([[1, 2, 3], [4, 5, 6]], &lt;type 'list'&gt;)
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test_type_conversion_array_int4
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---------------------------------
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{{1,2,3},{4,5,6}}
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(1 row)
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</programlisting>
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Other Python sequences, like tuples, are also accepted for
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backwards-compatibility with PostgreSQL versions 9.6 and below, when
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multi-dimensional arrays were not supported. However, they are always
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treated as one-dimensional arrays, because they are ambiguous with
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composite types. For the same reason, when a composite type is used in a
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multi-dimensional array, it must be represented by a tuple, rather than a
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list.
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</para>
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<para>
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Note that in Python, strings are sequences, which can have
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undesirable effects that might be familiar to Python programmers:
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@@ -541,14 +569,19 @@ CREATE TYPE named_value AS (
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CREATE FUNCTION make_pair (name text, value integer)
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RETURNS named_value
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AS $$
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return[ name, value]
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# or alternatively, as tuple: return( name, value)
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return( name, value)
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# or alternatively, as tuple: return[ name, value]
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$$ LANGUAGE plpythonu;
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</programlisting>
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To return a SQL null for any column, insert <symbol>None</symbol> at
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the corresponding position.
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</para>
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<para>
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When an array of composite types is returned, it cannot be returned as a list,
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because it is ambiguous whether the Python list represents a composite type,
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or another array dimension.
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</para>
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</listitem>
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</varlistentry>
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‎src/pl/plpython/expected/plpython_composite.out‎

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Original file line numberDiff line numberDiff line change
@@ -465,13 +465,13 @@ SELECT * FROM changing_test();
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-- tables of composite types
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CREATE FUNCTION composite_types_table(OUT tab table_record[], OUT typ type_record[] ) RETURNS SETOF record AS $$
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yield {'tab': [['first', 1], ['second', 2]],
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yield {'tab': [('first', 1), ('second', 2)],
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'typ': [{'first': 'third', 'second': 3},
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{'first': 'fourth', 'second': 4}]}
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yield {'tab': [['first', 1], ['second', 2]],
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yield {'tab': [('first', 1), ('second', 2)],
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'typ': [{'first': 'third', 'second': 3},
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{'first': 'fourth', 'second': 4}]}
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yield {'tab': [['first', 1], ['second', 2]],
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yield {'tab': [('first', 1), ('second', 2)],
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'typ': [{'first': 'third', 'second': 3},
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{'first': 'fourth', 'second': 4}]}
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$$ LANGUAGE plpythonu;
@@ -569,3 +569,13 @@ SELECT * FROM return_record_2('v3') AS (v1 int, v2 int, v3 int);
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1 | 2 | 3
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(1 row)
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-- multi-dimensional array of composite types.
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CREATE FUNCTION composite_type_as_list() RETURNS type_record[] AS $$
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return [[('first', 1), ('second', 1)], [('first', 2), ('second', 2)], [('first', 3), ('second', 3)]];
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$$ LANGUAGE plpython3u;
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SELECT * FROM composite_type_as_list();
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composite_type_as_list
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------------------------------------------------------------------------------------
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{{"(first,1)","(second,1)"},{"(first,2)","(second,2)"},{"(first,3)","(second,3)"}}
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(1 row)
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