astor – AST observe/rewrite





3-clause BSD

Build status:Travis CI

astor is designed to allow easy manipulation of Python source via the AST.

Getting Started

Install with pip:

$ pip install astor

or clone the latest version from GitHub.


There are some other similar libraries, but astor focuses on the following areas:

  • Round-trip back to Python via Armin Ronacher’s module:
    • Modified AST doesn’t need linenumbers, ctx, etc. or otherwise be directly compileable
    • Easy to read generated code as, well, code
  • Dump pretty-printing of AST
    • Harder to read than round-tripped code, but more accurate to figure out what is going on.
    • Easier to read than dump from built-in AST module
  • Non-recursive treewalk
    • Sometimes you want a recursive treewalk (and astor supports that, starting at any node on the tree), but sometimes you don’t need to do that. astor doesn’t require you to explicitly visit sub-nodes unless you want to:
    • You can add code that executes before a node’s children are visited, and/or
    • You can add code that executes after a node’s children are visited, and/or
    • You can add code that executes and keeps the node’s children from being visited (and optionally visit them yourself via a recursive call)
    • Write functions to access the tree based on object names and/or attribute names
    • Enjoy easy access to parent node(s) for tree rewriting



This section is not done. Please look at the source code for all public members.

astor.to_source(source, indent_with=' ' * 4, add_line_information=False)

Convert a node tree back into Python source code.

Each level of indentation is replaced with indent_with. Per default this parameter is equal to four spaces as suggested by PEP 8.

If add_line_information is set to True comments for the line numbers of the nodes are added to the output. This can be used to spot wrong line number information of statement nodes.