abc
– Psycopg abstract classes¶
The module exposes Psycopg definitions which can be used for static type checking.
- class psycopg.abc.Dumper(cls, context=None)¶
Convert Python objects of type cls to PostgreSQL representation.
- Parameters
cls (type) – The type that will be managed by this dumper.
context (
AdaptContext
or None) – The context where the transformation is performed. If not specified the conversion might be inaccurate, for instance it will not be possible to know the connection encoding or the server date format.
A partial implementation of this protocol (implementing everything except
dump()
) is available aspsycopg.adapt.Dumper
.- format: psycopg.pq.Format¶
The format that this class
dump()
method produces,TEXT
orBINARY
.This is a class attribute.
- dump(obj)¶
Convert the object obj to PostgreSQL representation.
- Parameters
obj (
Any
) – the object to convert.- Return type
The format returned by dump shouldn’t contain quotes or escaped values.
- quote(obj)¶
Convert the object obj to escaped representation.
- Parameters
obj (
Any
) – the object to convert.- Return type
Tip
This method will be used by
Literal
to convert a value client-side.This method only makes sense for text dumpers; the result of calling it on a binary dumper is undefined. It might scratch your car, or burn your cake. Don’t tell me I didn’t warn you.
- oid: int¶
The oid to pass to the server, if known; 0 otherwise (class attribute).
If the OID is not specified, PostgreSQL will try to infer the type from the context, but this may fail in some contexts and may require a cast (e.g. specifying
%s::type
for its placeholder).You can use the
psycopg.adapters
.
types
registry to find the OID of builtin types, and you can useTypeInfo
to extend the registry to custom types.
- get_key(obj, format)¶
Return an alternative key to upgrade the dumper to represent obj.
Normally the type of the object is all it takes to define how to dump the object to the database. For instance, a Python
date
can be simply converted into a PostgreSQLdate
.In a few cases, just the type is not enough. For example:
A Python
datetime
could be represented as atimestamptz
or atimestamp
, according to whether it specifies atzinfo
or not.A Python int could be stored as several Postgres types: int2, int4, int8, numeric. If a type too small is used, it may result in an overflow. If a type too large is used, PostgreSQL may not want to cast it to a smaller type.
Python lists should be dumped according to the type they contain to convert them to e.g. array of strings, array of ints (and which size of int?…)
In these cases, a dumper can implement
get_key()
and return a new class, or sequence of classes, that can be used to identify the same dumper again. If the mechanism is not needed, the method should return the same cls object passed in the constructor.If a dumper implements
get_key()
it should also implementupgrade()
.
- upgrade(obj, format)¶
Return a new dumper to manage obj.
Once
Transformer.get_dumper()
has been notified byget_key()
that this Dumper class cannot handle obj itself, it will invokeupgrade()
, which should return a newDumper
instance, which will be reused for every objects for whichget_key()
returns the same result.- Return type
- class psycopg.abc.Loader(oid, context=None)¶
Convert PostgreSQL values with type OID oid to Python objects.
- Parameters
oid (int) – The type that will be managed by this dumper.
context (
AdaptContext
or None) – The context where the transformation is performed. If not specified the conversion might be inaccurate, for instance it will not be possible to know the connection encoding or the server date format.
A partial implementation of this protocol (implementing everything except
load()
) is available aspsycopg.adapt.Loader
.- format: psycopg.pq.Format¶
The format that this class
load()
method can convert,TEXT
orBINARY
.This is a class attribute.
- class psycopg.abc.AdaptContext(*args, **kwargs)¶
A context describing how types are adapted.
Example of
AdaptContext
areConnection
,Cursor
,Transformer
,AdaptersMap
.Note that this is a
Protocol
, so objects implementingAdaptContext
don’t need to explicitly inherit from this class.See also
Data adaptation configuration for an explanation about how contexts are connected.
- property adapters: psycopg.adapt.AdaptersMap¶
The adapters configuration that this object uses.
- Return type
- property connection: Optional[psycopg.connection.BaseConnection[Any]]¶
The connection used by this object, if available.
- Return type
Connection
orAsyncConnection
orNone