Python流程语句：缩进与 if、while、for

• if[条件] … elif[条件] … else 条件控制语句：执行相应的条件语句。
• while [条件] … else 循环控制语句（无边界）：当条件为真时，则执行；条件为假，则不执行。
• for [条件] … else 循环控制语句（有边界）：同While。
• break/continue ：用于循环控制语句中。break为跳出当前循环，并结束循环；continue为从新进入循环条件判断。

#!/usr/bin/env python
# Filename: expression
 
running = True
number = int(input('Enter an integer: '))
again = 0
 
while running:
	if number == area:
		print 'Congratulations,you number it.' #New block starts here.
		print "(but you do not win any prizes!)" #New block ends here.
		running = False # this cause the while loop to stop
	elif number < area:
		print 'No, it is a little higher than that.' #Another block.
		# You can do whatever you want in a block ...
		number = number + 1
		again = again + 1
		print 'while running again, this',again,'agains.'
	else:
		print 'NO, it is a little lower than that.'
		# You must have number > aera to reach here.
		number = number - 1
		again = again + 1
		print 'while running again, this',again,'agains.'
else:
	print 'The while loop is over.'
	# Do anything else you want to do here .
 
pt = 0
fu = 0
# range(a,b,c).
# a is first print number .
# b is max number , but print number  not eq b .
# c is the print number length . 
# eg: print number = a + c , and a =< print number < b .
 
# break and continue for loop.
for i in range(0,again,1):
	pt = pt +1
	fu = fu + 2
	print 'The' , pt , "print number of 'for loop' is" , i ,'.'
	if pt > 3 :
		print "The loop of for will end to break stop."
		break
	elif pt == 3 :
		print "The loop of for will end last for again."
		continue
else:
	print 'The loop of for will end to normal.'