Flat code is better than nested. It's more readable, easier to update, and easier to debug. All of the linux kernel source code uses 8-space indents because, as I've seen it explained by Linus, if you can't use enough indents with 8-space, you have too many indents and need to refactor your code so it's more simple.
I do some data analysis type stuff at work fairly often. Sometimes I'll have a half-dozen conditional statements to satisfy in a loop where I'm ticking over rows of data. Using the "continue" statement is a really simple way to keep code flat and manageable.
Bad form would be like this:
for row in my_data:
if row[val] == 'blah':
if row[val2] == 'test':
doFunc(row)
doFunc2(row[val3])
if row[val3]:
yield row
Better would be like this:
for row in my_data:
if row[val] != 'blah':
continue
if row[val2] != 'test':
continue
doFunc(row)
doFunc2(row[val3])
if row[val3]:
yield row
