Is there any functional difference between the following two blocks of code? I'm concerned mainly with the order in which the functions are called. Are functions executed sequentially in the first if statement?
First,
if func1() and func2() and func3() and func4():
do stuff
Second,
if func1():
if func2():
if func3():
if func4():
do stuff
Yes, Python evaluates expressions from left to right. The functions will be called in the same order. From the reference documentation:
Python evaluates expressions from left to right.
Moreover, func2() will not be called if func1() returned a false value, both when using and and when nesting if expressions. Quoting the boolean operations documentation:
The expression
x and yfirst evaluatesx; ifxis false, its value is returned; otherwise,yis evaluated and the resulting value is returned.
Because in the expression func1() and func2(), func2() will not be evaluated if func1() returned a false value, func2() is not called at all.
You could use a third alternative here using the all() function:
functions = (func1, func2, func3, func4)
if all(f() for f in functions):
which would again only call functions as long as the preceding function returned a true value and call the functions in order.
The all() approach does require that func1, func2, func3, and func4 are all actually defined before you call all(), while the nested if or and expression approaches only require functions to be defined as long as the preceding function returned a true value.
func2() won't be even looked up if func1() returns false, so that code works even if func2 isn't defined, while the all() approach will fail with a NameError if func2 can't be found.