how to stop a for loop
Use break
and continue
to do this. Breaking nested loops can be done in Python using the following:
for a in range(...):
for b in range(..):
if some condition:
# break the inner loop
break
else:
# will be called if the previous loop did not end with a `break`
continue
# but here we end up right after breaking the inner loop, so we can
# simply break the outer loop as well
break
Another way is to wrap everything in a function and use return
to escape from the loop.
There are several ways to do it:
The simple Way: a sentinel variable
n = L[0][0]
m = len(A)
found = False
for i in range(m):
if found:
break
for j in range(m):
if L[i][j] != n:
found = True
break
Pros: easy to understand Cons: additional conditional statement for every loop
The hacky Way: raising an exception
n = L[0][0]
m = len(A)
try:
for x in range(3):
for z in range(3):
if L[i][j] != n:
raise StopIteration
except StopIteration:
pass
Pros: very straightforward Cons: you use Exception outside of their semantic
The clean Way: make a function
def is_different_value(l, elem, size):
for x in range(size):
for z in range(size):
if l[i][j] != elem:
return True
return False
if is_different_value(L, L[0][0], len(A)):
print "Doh"
pros: much cleaner and still efficient cons: yet feels like C
The pythonic way: use iteration as it should be
def is_different_value(iterable):
first = iterable[0][0]
for l in iterable:
for elem in l:
if elem != first:
return True
return False
if is_different_value(L):
print "Doh"
pros: still clean and efficient cons: you reinvdent the wheel
The guru way: use any()
:
def is_different_value(iterable):
first = iterable[0][0]
return any(cell != first for col in iterable for cell in col)
if is_different_value(L):
print "Doh"
pros: you'll feel empowered with dark powers cons: people that will read you code may start to dislike you
Try to simply use break statement.
Also you can use the following code as an example:
a = [[0,1,0], [1,0,0], [1,1,1]]
b = [[0,0,0], [0,0,0], [0,0,0]]
def check_matr(matr, expVal):
for row in matr:
if len(set(row)) > 1 or set(row).pop() != expVal:
print 'Wrong'
break# or return
else:
print 'ok'
else:
print 'empty'
check_matr(a, 0)
check_matr(b, 0)