There are two types of loops in Python, for and while.
The "for" loop
For loops iterate over a given sequence. Here is an example:
primes = [2,3,5,7] for prime in primes: print prime
For loops can iterate over a sequence of numbers using the "range" and "xrange" functions. The difference between range and xrange is that the range function returns a new list with numbers of that specified range, whereas xrange returns an iterator, which is more efficient. (Python 3 uses the range function, which acts like xrange). Note that the xrange function is zero based.
# Prints out the numbers 0,1,2,3,4 for x in xrange(5): print x # Prints out 3,4,5 for x in xrange(3,6): print x
While loops repeat as long as a certain boolean condition is met. For example:
# Prints out 0,1,2,3,4 count = 0 while count < 5: print count count += 1 # This is the same as count = count + 1
"break" and "continue" statements
break is used to exit a for loop or a while loop, whereas continue is used to skip the current block, and return to the "for" or "while" statement. A few examples:
# Prints out 0,1,2,3,4 count = 0 while True: print count count += 1 if count >= 5: break # Prints out only odd numbers - 1,3,5,7,9 for x in xrange(10): # Check if x is even if x % 2 == 0: continue print x
Loop through and print out all even numbers from the numbers list in the same order they are received. Don't print any numbers that come after 237 in the sequence.