GNU Info

(python2.1-ref.info)exec statement

---

Prev: global statement Up: Simple statements

---

Enter node , (file) or (file)node

The `exec' statement
====================

     exec_stmt:    "exec" expression ["in" expression ["," expression]]

This statement supports dynamic execution of Python code.  The first
expression should evaluate to either a string, an open file object, or
a code object.  If it is a string, the string is parsed as a suite of
Python statements which is then executed (unless a syntax error
occurs).  If it is an open file, the file is parsed until EOF and
executed.  If it is a code object, it is simply executed.

In all cases, if the optional parts are omitted, the code is executed
in the current scope.  If only the first expression after `in' is
specified, it should be a dictionary, which will be used for both the
global and the local variables.  If two expressions are given, both
must be dictionaries and they are used for the global and local
variables, respectively.

As a side effect, an implementation may insert additional keys into the
dictionaries given besides those corresponding to variable names set by
the executed code.  For example, the current implementation may add a
reference to the dictionary of the built-in module `__builtin__' under
the key `__builtins__' (!).

*Programmer's hints:* dynamic evaluation of expressions is supported by
the built-in function `eval()'.  The built-in functions `globals()' and
`locals()' return the current global and local dictionary,
respectively, which may be useful to pass around for use by `exec'.

Also, in the current implementation, multi-line compound statements must
end with a newline: `exec "for v in seq:\n\tprint v\n"' works, but
`exec "for v in seq:\n\tprint v"' fails with `SyntaxError'.