for loops can be used to step through lists, tuples, and other ’iterable’ objects.
Iterating through a list:
for item in [10,25,50,75,100]: print (item, item**2) OUT: 10 100 25 625 50 2500 75 5625 100 10000
A for loop may be used to generate and loop through a sequence of numbers (note that a ’range’ does not include the maximum value specified):
for i in range(100,150,10): print(i) OUT: 100 110 120 130 140
A for loop may be used to loop through an index of positions in a list:
my_list = ['Frodo','Bilbo','Gandalf','Gimli','Sauron'] for i in range(len(my_list)): print ('Index:',i,', Value',my_list[i]) OUT: Index: 0 , Value Frodo Index: 1 , Value Bilbo Index: 2 , Value Gandalf Index: 3 , Value Gimli Index: 4 , Value Sauron
Breaking out of loops or continuing the loop without action
Though it may not be considered best coding practice, it is possible to prematurely escape a loop with the break command:
for i in range(10): # This loop would normally go from 0 to 9 if i == 5: break else: print(i) print ('Loop complete') OUT: 0 1 2 3 4 Loop complete
Or, rather than breaking out of a loop, it is possible to effectively skip an iteration of a loop with the continue command. This may be places anywhere in the loop and returns the focus to the start of the loop.
for i in range (10): if i%2 == 0: # This is the integer remainder after dividing i by 2 continue else: print (i) print ('Loop complete') OUT: 1 3 5 7 9 Loop complete
Using pass to replace active code in a loop
The pass command is most useful as a place holder to allow a loop to be built and have contents added later.
for i in range (10): # Some code will be added here later pass print ('Loop complete') OUT: Loop complete