polars.Expr.str.zfill#

Expr.str.zfill(length: int | IntoExprColumn) → Expr[source]#

Pad the start of the string with zeros until it reaches the given length.

A sign prefix (-) is handled by inserting the padding after the sign character rather than before.

Parameters:

length: Pad the string until it reaches this length. Strings with length equal to or greater than this value are returned as-is.

See also

pad_start

Notes

This method is intended for padding numeric strings. If your data contains non-ASCII characters, use pad_start() instead.

Examples

>>> df = pl.DataFrame({"a": [-1, 123, 999999, None]})
>>> df.with_columns(zfill=pl.col("a").cast(pl.String).str.zfill(4))
shape: (4, 2)
┌────────┬────────┐
│ a      ┆ zfill  │
│ ---    ┆ ---    │
│ i64    ┆ str    │
╞════════╪════════╡
│ -1     ┆ -001   │
│ 123    ┆ 0123   │
│ 999999 ┆ 999999 │
│ null   ┆ null   │
└────────┴────────┘
>>> df = pl.DataFrame(
...     {
...         "a": [-1, 123, 999999, None],
...         "length": [8, 4, 1, 2],
...     }
... )
>>> df.with_columns(zfill=pl.col("a").cast(pl.String).str.zfill("length"))
shape: (4, 3)
┌────────┬────────┬──────────┐
│ a      ┆ length ┆ zfill    │
│ ---    ┆ ---    ┆ ---      │
│ i64    ┆ i64    ┆ str      │
╞════════╪════════╪══════════╡
│ -1     ┆ 8      ┆ -0000001 │
│ 123    ┆ 4      ┆ 0123     │
│ 999999 ┆ 1      ┆ 999999   │
│ null   ┆ 2      ┆ null     │
└────────┴────────┴──────────┘