Python Library Reference

Next: 3.15.3 Queries on AST Up: 3.15 parser Previous: 3.15.1 Creating AST Objects

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3.15.2 Converting AST Objects

AST objects, regardless of the input used to create them, may be converted to parse trees represented as list- or tuple- trees, or may be compiled into executable code objects. Parse trees may be extracted with or without line numbering information.

ast2list (ast[, line_info])

This function accepts an AST object from the caller in ast and returns a Python list representing the equivalent parse tree. The resulting list representation can be used for inspection or the creation of a new parse tree in list form. This function does not fail so long as memory is available to build the list representation. If the parse tree will only be used for inspection, ast2tuple() should be used instead to reduce memory consumption and fragmentation. When the list representation is required, this function is significantly faster than retrieving a tuple representation and converting that to nested lists.

If line_info is true, line number information will be included for all terminal tokens as a third element of the list representing the token. Note that the line number provided specifies the line on which the token ends. This information is omitted if the flag is false or omitted.

ast2tuple (ast[, line_info])

This function accepts an AST object from the caller in ast and returns a Python tuple representing the equivalent parse tree. Other than returning a tuple instead of a list, this function is identical to ast2list().

If line_info is true, line number information will be included for all terminal tokens as a third element of the list representing the token. This information is omitted if the flag is false or omitted.

compileast (ast[, filename = '<ast>'])

The Python byte compiler can be invoked on an AST object to produce code objects which can be used as part of an exec statement or a call to the built-in eval() function. This function provides the interface to the compiler, passing the internal parse tree from ast to the parser, using the source file name specified by the filename parameter. The default value supplied for filename indicates that the source was an AST object.

Compiling an AST object may result in exceptions related to compilation; an example would be a SyntaxError caused by the parse tree for del f(0): this statement is considered legal within the formal grammar for Python but is not a legal language construct. The SyntaxError raised for this condition is actually generated by the Python byte-compiler normally, which is why it can be raised at this point by the parser module. Most causes of compilation failure can be diagnosed programmatically by inspection of the parse tree.

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Python Library Reference

Next: 3.15.3 Queries on AST Up: 3.15 parser Previous: 3.15.1 Creating AST Objects