Am Wed, 05 Sep 2007 13:12:24 +0000 schrieb [EMAIL PROTECTED]: > I am completely puzzled why the following exec code does not work: > > mycode = "import math\ndef f(y):\n print math.floor(y)\nf(3.14)" > def execute(): > exec mycode > execute() > > > I get the error: > > [EMAIL PROTECTED]:/opt/qbase# python error1.py > Traceback (most recent call last): > File "error1.py", line 5, in ? > execute() > File "error1.py", line 4, in execute > exec mycode > File "<string>", line 4, in ? > File "<string>", line 3, in f > NameError: global name 'math' is not defined > Note that the following code _does_ work: > > mycode = "import math\ndef f(y):\n print math.floor(y)\nf(3.14)" > exec mycode > I have tested this in python 2.3 and 2.4.
exec breaks nested namespaces here. Essentially exec "import math" puts the "math" name into the local namespace, but "def f(): math.floor" looks up "math" in the global namespace. On the module level global and local namespace are identical >>> globals() is locals() True but inside a function they are distinct >>> def f(): return globals() is locals() ... >>> f() False A workaround is to declare "math" as global: >>> s = """ ... global math ... import math ... def f(y): print math.floor(y) ... f(3.14) ... """ >>> def execute(): ... exec s ... >>> execute() 3.0 or pass it explicitly: [new interpreter session] >>> s = """ ... import math ... def f(y, math=math): print math.floor(y) ... f(3.14) ... """ >>> def execute(): ... exec s ... >>> execute() 3.0 Peter -- http://mail.python.org/mailman/listinfo/python-list
