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Diffstat (limited to 'Doc')
| -rw-r--r-- | Doc/library/_ast.rst | 27 |
1 files changed, 25 insertions, 2 deletions
diff --git a/Doc/library/_ast.rst b/Doc/library/_ast.rst index e9f4ad4..80b8a37 100644 --- a/Doc/library/_ast.rst +++ b/Doc/library/_ast.rst @@ -46,9 +46,32 @@ node. The utf8 offset is recorded because the parser uses utf8 internally. If these attributes are marked as optional in the grammar (using a question mark), the value might be ``None``. If the attributes can have zero-or-more values (marked with an asterisk), the values are represented as Python lists. +All possible attributes must be present and have valid values when compiling an +AST with :func:`compile`. + +The constructor of a class ``_ast.T`` parses their arguments as follows: + +* If there are positional arguments, there must be as many as there are items in + ``T._fields``; they will be assigned as attributes of these names. +* If there are keyword arguments, they will set the attributes of the same names + to the given values. + +For example, to create and populate a ``UnaryOp`` node, you could use :: + + node = _ast.UnaryOp() + node.op = _ast.USub() + node.operand = _ast.Num() + node.operand.n = 5 + node.operand.lineno = 0 + node.operand.col_offset = 0 + node.lineno = 0 + node.col_offset = 0 + +or the more compact :: + + node = _ast.UnaryOp(_ast.USub(), _ast.Num(5, lineno=0, col_offset=0), + lineno=0, col_offset=0) -The constructors of all ``_ast`` classes don't take arguments; instead, if you -create instances, you must assign the required attributes separately. Abstract Grammar |