Question :
C doesn’t guarantee any evaluation order so a statement like f(g1()+g2(), g3(), g4()) might execute g1(), g2(), g3(), and g4() in any order (although f() would be executed after all of them)
What about Python? My experimentation for Python 2.7 shows that it appears to be left-to-right order of evaluation but I wonder if this is specified to be the case.
Test program:
def somefunc(prolog, epilog):
print prolog
def f(a, b, *args):
print epilog
return f
def f(text):
print text
return 1
somefunc('f1','f2')(f('hey'),f('ho'),f('hahaha'),f('tweedledee')+f('tweedledum'))
which prints
f1
hey
ho
hahaha
tweedledee
tweedledum
f2
Answer #1:
Yes, left to right evaluation order is guaranteed, with the exception of assignments. That’s documented here (py2, py3):
Python evaluates expressions from left to right. Notice that while evaluating an assignment, the right-hand side is evaluated before the left-hand side.
In the following lines, expressions will be evaluated in the arithmetic order of their suffixes:
expr1, expr2, expr3, expr4
(expr1, expr2, expr3, expr4)
{expr1: expr2, expr3: expr4}
expr1 + expr2 * (expr3 - expr4)
expr1(expr2, expr3, *expr4, **expr5)
expr3, expr4 = expr1, expr2
If the language were not making some choice about this, the evaluation of one argument could mutate another argument and result in unspecified behaviour, so all implementations of Python must follow this spec.
Answer #2:
https://docs.python.org/3/reference/expressions.html#evaluation-order:
Python evaluates expressions from left to right. Notice that while
evaluating an assignment, the right-hand side is evaluated before the
left-hand side.In the following lines, expressions will be evaluated in the
arithmetic order of their suffixes:expr1, expr2, expr3, expr4 (expr1, expr2, expr3, expr4) {expr1: expr2, expr3: expr4} expr1 + expr2 * (expr3 - expr4) expr1(expr2, expr3, *expr4, **expr5) expr3, expr4 = expr1, expr2
