Pandas.eval replacement in polars

Question

Suppose I have an expression like "col3 = col2 + col1" so pandas we can directly call pandas.dataframe.eval() but in polars I cannot find such method.

I have series.eval in polars but no luck as I want evaluate user given expression on a dataframe.

Answer 1

Acception strings

You can pass SQL to pl.sql_expr.

df = pl.DataFrame({
    "col1": [1, 2],
    "col2": [1, 2],
})
df.select(
    pl.sql_expr("col2 + col1 as col3")
)

Or you can run a complete SQL query with pl.sql

pl.sql("SELECT col2 + col1 as col3 FROM df").collect()

shape: (2, 1)
┌──────┐
│ col3 │
│ ---  │
│ i64  │
╞══════╡
│ 2    │
│ 4    │
└──────┘

Accept expressions directly

i want evaluate user given expression on a dataframe.

I would accept pl.Expression directly instead of strings. This gives more type safety than strings and probably also a better user experience as you can have autocomplete and the IDE may show available methods/arguments.