polars.dtype_of

polars.dtype_of(col_or_expr: str | Expr) → DataTypeExpr

Get a lazily evaluated DataType of a column or expression.

Warning

This functionality is considered unstable. It may be changed at any point without it being considered a breaking change.

Examples

>>> def inspect(expr: pl.Expr) -> pl.Expr:
...     def print_and_return(s: pl.Series) -> pl.Series:
...         print(s)
...         return s
...
...     return expr.map_batches(
...         print_and_return,
...         # Clarify that the expression returns the same datatype as the input
...         # datatype.
...         return_dtype=pl.dtype_of(expr),
...     )
>>> df = pl.DataFrame(
...     {
...         "UserID": [1, 2, 3, 4, 5],
...         "Name": ["Alice", "Bob", "Charlie", "Diana", "Ethan"],
...     }
... )
>>> df.select(inspect(pl.col("Name")))
shape: (5,)
Series: 'Name' [str]
[
    "Alice"
    "Bob"
    "Charlie"
    "Diana"
    "Ethan"
]
shape: (5, 1)
┌─────────┐
│ Name    │
│ ---     │
│ str     │
╞═════════╡
│ Alice   │
│ Bob     │
│ Charlie │
│ Diana   │
│ Ethan   │
└─────────┘