polars.Expr.meta.output_name#

Expr.meta.output_name(*, raise_if_undetermined: bool = True) → str | None[source]#

Get the column name that this expression would produce.

It may not always be possible to determine the output name as that can depend on the schema of the context; in that case this will raise ComputeError if raise_if_undetermined is True (the default), or None otherwise.

Examples

>>> e = pl.col("foo") * pl.col("bar")
>>> e.meta.output_name()
'foo'
>>> e_filter = pl.col("foo").filter(pl.col("bar") == 13)
>>> e_filter.meta.output_name()
'foo'
>>> e_sum_over = pl.sum("foo").over("groups")
>>> e_sum_over.meta.output_name()
'foo'
>>> e_sum_slice = pl.sum("foo").slice(pl.len() - 10, pl.col("bar"))
>>> e_sum_slice.meta.output_name()
'foo'
>>> pl.len().meta.output_name()
'len'