Visitor and Traversal Utilities¶
The sqlalchemy.sql.visitors module consists of classes and functions
that serve the purpose of generically traversing a Core SQL expression
structure. This is not unlike the Python ast module in that is presents
a system by which a program can operate upon each component of a SQL
expression. Common purposes this serves are locating various kinds of
elements such as Table or BindParameter objects,
as well as altering the state of the structure such as replacing certain FROM
clauses with others.
Note
the sqlalchemy.sql.visitors module is an internal API and
is not fully public. It is subject to change and may additionally not
function as expected for use patterns that aren’t considered within
SQLAlchemy’s own internals.
The sqlalchemy.sql.visitors module is part of the internals of
SQLAlchemy and it is not usually used by calling application code. It is
however used in certain edge cases such as when constructing caching routines
as well as when building out custom SQL expressions using the
Custom SQL Constructs and Compilation Extension.