You can use the eval(string)
method to do this.
Definition
eval(code, globals=None, locals=None)
The code is just standard Python code - this means that it still needs to be properly indented.
The globals can have a custom __builtins__
defined, which could be useful for security purposes.
Example
eval("print('Hello')")
Would print hello
to the console. You can also specify local and global variables for the code to use:
eval("print('Hello, %s'%name)", {}, {'name':'person-b'})
Security Concerns
Be careful, though. Any user input will be executed. Consider:
eval("import os;os.system('sudo rm -rf /')")
There are a number of ways around that. The easiest is to do something like:
eval("import os;...", {'os':None})
Which will throw an exception, rather than erasing your hard drive. While your program is desktop, this could be a problem if people redistributed scripts, which I imagine is intended.
Strange Example
Here's an example of using eval
rather strangely:
def hello() : print('Hello')
def world() : print('world')
CURRENT_MOOD = 'happy'
eval(get_code(), {'contrivedExample':__main__}, {'hi':hello}.update(locals()))
What this does on the eval line is:
- Gives the current module another name (it becomes
contrivedExample
to the script). The consumer can call contrivedExample.hello()
now.)
- It defines
hi
as pointing to hello
- It combined that dictionary with the list of current globals in the executing module.
FAIL
It turns out (thanks commenters!) that you actually need to use the exec
statement. Big oops. The revised examples are as follows:
exec
Definition
(This looks familiar!)
Exec is a statement:
exec "code" [in scope]
Where scope is a dictionary of both local and global variables. If this is not specified, it executes in the current scope.
The code is just standard Python code - this means that it still needs to be properly indented.
exec
Example
exec "print('hello')"
Would print hello
to the console. You can also specify local and global variables for the code to use:
eval "print('hello, '+name)" in {'name':'person-b'}
exec
Security Concerns
Be careful, though. Any user input will be executed. Consider:
exec "import os;os.system('sudo rm -rf /')"
Print Statement
As also noted by commenters, print
is a statement in all versions of Python prior to 3.0. In 2.6, the behaviour can be changed by typing from __future__ import print_statement
. Otherwise, use:
print "hello"
Instead of :
print("hello")