Databases
StackOverflow2013
Postsdbo
POIs it possible to modify the return value of a function without defining new function in python?
Body
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POIs it possible to modify the return value of a function without defining new function in python?
    text
    copied!<pre><code>def foo(a, b, c = 0): return a+b </code></pre> <p>I have dozens of functions like 'foo', which all have different argument numbers and names. Is there a common way that I can get the return values of these functions and do just a single extra operation like pformat to them?</p> <p>Yes I can just generate a new function like the following:</p> <pre><code>func = ... # func can be got using getattr by name def wrapper(*arg, **kw): data = func(*arg, **kw) return pprint.pformat(data) return wrapper </code></pre> <p>But then the new function 'wrapper' is different to the old one 'func', for example, in argument number, 'wrapper' has only 2 args--'arg' and 'kw', but 'func' may have many args, like 'a', 'b', 'c'.</p> <p>I just want play with the return value, everything else should stay still, is it possible?</p> <p>Thanks!</p> <p><strong>Update</strong> Finally this problem was solved using <a href="http://pypi.python.org/pypi/decorator/3.2.0" rel="nofollow">decorator</a> module and the following patch:</p> <pre><code>--- /home/jaime/cache/decorator-3.2.0/src/decorator.py 2010-05-22 23:53:46.000000000 +0800 +++ decorator.py 2010-10-28 14:55:11.511140589 +0800 @@ -66,9 +66,12 @@ self.name = '_lambda_' self.doc = func.__doc__ self.module = func.__module__ - if inspect.isfunction(func): + if inspect.isfunction(func) or inspect.ismethod(func): argspec = inspect.getargspec(func) self.args, self.varargs, self.keywords, self.defaults = argspec + if inspect.ismethod(func): + self.args = self.args[1:] # Remove the useless 'self' arg + argspec = inspect.ArgSpec(self.args, self.varargs, self.keywords, self.defaults) for i, arg in enumerate(self.args): setattr(self, 'arg%d' % i, arg) self.signature = inspect.formatargspec( </code></pre> <p>This patch allows you to decorate bounded methods, it just throws the first 'self' argument away, usage of decorator.decorator stays the same, no bad effects found right now.</p> <p>example code:</p> <pre><code>def __getattr__(self, attr): def pformat_wrapper(f, *args, **kw): data = f(*args, **kw) return pprint.pformat(data, indent = 4) method = getattr(self.ncapi, attr) return decorator(pformat_wrapper, method) # Signature preserving decorating jaime@westeros:~/bay/dragon.testing/tests$ python Python 2.6.5 (r265:79063, Apr 16 2010, 13:09:56) [GCC 4.4.3] on linux2 Type "help", "copyright", "credits" or "license" for more information. &gt;&gt;&gt; import decorator &gt;&gt;&gt; class A: ... def f(self): ... pass ... &gt;&gt;&gt; a = A() &gt;&gt;&gt; a.f &lt;bound method A.f of &lt;__main__.A instance at 0xb774a20c&gt;&gt; &gt;&gt;&gt; def hello(f, *args, **kw): ... print 'hello' ... return f(*args, **kw) ... &gt;&gt;&gt; f1 = decorator.decorator(hello, a.f) &gt;&gt;&gt; f1() hello &gt;&gt;&gt; </code></pre>
 

Querying!

 
Guidance
An individual column

Larger individual text columns get their own page to allow for proper reading.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload