README.md

Substrait

A Python package for Substrait, the cross-language specification for data compute operations.

Installation

You can install the Python substrait bindings from PyPI or conda-forge

pip install substrait

conda install -c conda-forge python-substrait  # or use mamba

Goals

This project aims to provide a Python interface for the Substrait specification. It will allow users to construct and manipulate a Substrait Plan from Python for evaluation by a Substrait consumer, such as DataFusion or DuckDB.

Non-goals

This project is not an execution engine for Substrait Plans.

Status

This is an experimental package that is still under development.

Example

Produce a Substrait Plan

The substrait.proto module provides access to the classes that represent a substrait Plan, thus allowing to create new plans.

Here is an example plan equivalent to SELECT first_name FROM person where people table has first_name and surname columns of type String

>>> from substrait import proto
>>> plan = proto.Plan(
...   relations=[
...     proto.PlanRel(
...       root=proto.RelRoot(
...         names=["first_name"], 
...         input=proto.Rel(
...           read=proto.ReadRel(
...             named_table=proto.ReadRel.NamedTable(names=["people"]),
...             base_schema=proto.NamedStruct(
...               names=["first_name", "surname"], 
...               struct=proto.Type.Struct(
...                 types=[
...                   proto.Type(string=proto.Type.String(nullability=proto.Type.Nullability.NULLABILITY_REQUIRED)), 
...                   proto.Type(string=proto.Type.String(nullability=proto.Type.Nullability.NULLABILITY_REQUIRED))
...                 ]  # /types
...               )  # /struct
...             )  # /base_schema
...           )  # /read
...         )  # /input
...       )  # /root
...     )  # /PlanRel
...   ]  # /relations
... )
>>> print(plan)
relations {
  root {
    input {
      read {
        base_schema {
          names: "first_name"
          names: "surname"
          struct {
            types {
              string {
                nullability: NULLABILITY_REQUIRED
              }
            }
            types {
              string {
                nullability: NULLABILITY_REQUIRED
              }
            }
          }
        }
        named_table {
          names: "people"
        }
      }
    }
    names: "first_name"
  }
}
>>> serialized_plan = p.SerializeToString()
>>> serialized_plan
b'\x1aA\x12?\n1\n/\x12#\n\nfirst_name\n\x07surname\x12\x0c\n\x04b\x02\x10\x02\n\x04b\x02\x10\x02:\x08\n\x06people\x12\nfirst_name'

Consume the Substrait Plan

The same plan we generated in the previous example, can be loaded back from its binary representation using the Plan.ParseFromString method:

>>> from substrait.proto import Plan
>>> p = Plan()
>>> p.ParseFromString(serialized_plan)
67
>>> p
relations {
  root {
    input {
      read {
        base_schema {
          names: "first_name"
          names: "surname"
          struct {
            types {
              string {
                nullability: NULLABILITY_REQUIRED
              }
            }
            types {
              string {
                nullability: NULLABILITY_REQUIRED
              }
            }
          }
        }
        named_table {
          names: "people"
        }
      }
    }
    names: "first_name"
  }
}

Load a Substrait Plan from JSON

A substrait plan can be loaded from its JSON representation using the substrait.json.load_json and substrait.json.parse_json functions:

>>> import substrait.json
>>> jsontext = """{
...   "relations":[
...     {
...       "root":{
...         "input":{
...           "read":{
...             "baseSchema":{
...               "names":[
...                 "first_name",
...                 "surname"
...               ],
...               "struct":{
...                 "types":[
...                   {
...                     "string":{
...                       "nullability":"NULLABILITY_REQUIRED"
...                     }
...                   },
...                   {
...                     "string":{
...                       "nullability":"NULLABILITY_REQUIRED"
...                     }
...                   }
...                 ]
...               }
...             },
...             "namedTable":{
...               "names":[
...                 "people"
...               ]
...             }
...           }
...         },
...         "names":[
...           "first_name"
...         ]
...       }
...     }
...   ]
... }"""
>>> substrait.json.parse_json(jsontext)
relations {
  root {
    input {
      read {
        base_schema {
          names: "first_name"
          names: "surname"
          struct {
            types {
              string {
                nullability: NULLABILITY_REQUIRED
              }
            }
            types {
              string {
                nullability: NULLABILITY_REQUIRED
              }
            }
          }
        }
        named_table {
          names: "people"
        }
      }
    }
    names: "first_name"
  }
}

Produce a Substrait Plan with Ibis

Let's use an existing Substrait producer, Ibis, to provide an example using Python Substrait as the consumer.

In [1]: import ibis

In [2]: movie_ratings = ibis.table(
   ...:     [
   ...:         ("tconst", "str"),
   ...:         ("averageRating", "str"),
   ...:         ("numVotes", "str"),
   ...:     ],
   ...:     name="ratings",
   ...: )
   ...:

In [3]: query = movie_ratings.select(
   ...:     movie_ratings.tconst,
   ...:     avg_rating=movie_ratings.averageRating.cast("float"),
   ...:     num_votes=movie_ratings.numVotes.cast("int"),
   ...: )

In [4]: from ibis_substrait.compiler.core import SubstraitCompiler

In [5]: compiler = SubstraitCompiler()

In [6]: protobuf_msg = compiler.compile(query).SerializeToString()

In [7]: from substrait.proto import Plan

In [8]: my_plan = Plan()

In [9]: my_plan.ParseFromString(protobuf_msg)
Out[9]: 186

In [10]: print(my_plan)
relations {
  root {
    input {
      project {
        common {
          emit {
            output_mapping: 3
            output_mapping: 4
            output_mapping: 5
          }
        }
        input {
          read {
            common {
              direct {
              }
            }
            base_schema {
              names: "tconst"
              names: "averageRating"
              names: "numVotes"
              struct {
                types {
                  string {
                    nullability: NULLABILITY_NULLABLE
                  }
                }
                types {
                  string {
                    nullability: NULLABILITY_NULLABLE
                  }
                }
                types {
                  string {
                    nullability: NULLABILITY_NULLABLE
                  }
                }
                nullability: NULLABILITY_REQUIRED
              }
            }
            named_table {
              names: "ratings"
            }
          }
        }
        expressions {
          selection {
            direct_reference {
              struct_field {
              }
            }
            root_reference {
            }
          }
        }
        expressions {
          cast {
            type {
              fp64 {
                nullability: NULLABILITY_NULLABLE
              }
            }
            input {
              selection {
                direct_reference {
                  struct_field {
                    field: 1
                  }
                }
                root_reference {
                }
              }
            }
            failure_behavior: FAILURE_BEHAVIOR_THROW_EXCEPTION
          }
        }
        expressions {
          cast {
            type {
              i64 {
                nullability: NULLABILITY_NULLABLE
              }
            }
            input {
              selection {
                direct_reference {
                  struct_field {
                    field: 2
                  }
                }
                root_reference {
                }
              }
            }
            failure_behavior: FAILURE_BEHAVIOR_THROW_EXCEPTION
          }
        }
      }
    }
    names: "tconst"
    names: "avg_rating"
    names: "num_votes"
  }
}
version {
  minor_number: 24
  producer: "ibis-substrait"
}