python symbol can be global and local in the same scope

Question

Consider this function:

def content(path):
  global file # not useful but valid
  with open(path) as file:
    return file.read()

When generating a symbol table (using module symtable ) and inspecting the symbol file in the scope of the function content , it is global and local at the same time. After calling this function the global name file is bound to the file object. So I wonder why the symbol file in the function scope is also considered as a local symbol?

Here is code to reproduce the behaviour (put it in a file eg called global_and_local.py ):

import symtable

def content(path):
  global file
  with open(path) as file:
    return file.read()

symtable_root = symtable.symtable(content(__file__), __file__, "exec")
symtable_function = symtable_root.get_children()[0]
symbol_file = symtable_function.lookup('file')
print("symbol 'file' in function scope: is_global() =", symbol_file.is_global())
print("symbol 'file' in function scope: is_local() =", symbol_file.is_local())
print("global scope: file =", file)

The following output is generated:

symbol 'file' in function scope: is_global() = True
symbol 'file' in function scope: is_local() = True
global scope: file = <_io.TextIOWrapper name='global_and_local.py' ...>

Answer 1

For some reason, symtable defines is_local as a check for whether any binding operations for a symbol occur in the scope (or annotations, which are lumped together with annotated assignments at this stage):

def is_local(self):
    return bool(self.__flags & DEF_BOUND)

rather than a check for whether the symbol is actually local, which would look like

def is_local(self):
    return bool(self.__scope in (LOCAL, CELL))

I'm not sure why. This might be a bug. I don't think modules like this get much use - it took over a year before anyone noticed that adding the // operator broke the old parser module, so I could easily see this going unnoticed.