On 6/9/2017 6:00 PM, Erik wrote:
On 09/06/17 19:39, sondes kalboussi wrote:
Am a bit confused I was thinking that the order of execution of
functions in a code is from the first to the last function but
sometimes it is the opposite, for instance, some parameters or
outputs from the second function are called in the first one even
thou they are not global, any hints ?
As a complete and utter guess, I assume you are talking about something
like:
result = func1(1, 2, func2(x, y))
On the right side of '=', Python evaluates expressions, to the extent
possible, left to right. The result of each evaluation is an object.
In the above, the order is func1, 1, 2, func2, x, y, _tem = func2(x, y),
func1(1, 2, _tem). Note that function expressions can be more
complicated than just a name, as in func_array[selector].
In this case, func2() will be called before func1(). This is because
func1() needs three parameters and one of those parameters is the return
value of func2().
Given r = f[a](1, g[b](c)), your rule above does not determine whether
f[a] or g[b] is determined first. In at least some C implementations,
g[b] would be. Since the call g[b](c) could affect the bindings of f,
a, and the result of f[a], the rule that f[a] is calculated before g, b,
c, g[b], and g[b](c) may make a real difference.
Python can not know the return value of func2() without calling it.
Therefore, to be able to call func1() and give it its three parameters,
it must first call func2() to find out what that third parameter value is.
It's equivalent to:
func2result = func2(x, y)
result = func1(1, 2, func2result)
Since the func2 call could have the side effect of rebinding 'func1',
this is not exactly equivalent.
If that is _not_ what you are talking about, then like Thomas says - you
need to paste some code and explain what you are confused by.
Indeed.
--
Terry Jan Reedy
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