1. And now for something completely different . . .
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2. Part 5 Python 3 - Repetition and String Formatting
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3. Python 3 Repetition and String Formatting
The while loop
The for loop
String formatting
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4. Python Repetition and String Formatting
The while loop
The for loop
String formatting
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5. The while statement
Like the if statement, the while statement makes use of a Boolean expression...
x = 1
while x < 5:
print ('Hi spam')
x = x + 1
print ('done')
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6. The while statement
The Boolean expression (condition) in this example is:
x < 5
The expression has a value of true or false (1 or 0).
x = 1
while x < 5:
print ('Hi spam')
x = x + 1
print ('done')
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7. The while statement
If the condition is true, the indented statements are executed, otherwise, the statements are skipped.
x = 1
while x < 5:
print ('Hi spam')
x = x + 1
print ('done')
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8. The while statement 05-01.py 05-02.py x = 1 while x < 5:
print ('Hi spam')
x = x - 1
print ('done')
05-01.py
05-02.py
These programs are examples of counter-controlled while loops.
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9. The infinite while loop
print ('Hi spam')
print ('done')
05-03.py
05-04.py
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10. The break statement 05-05.py while 1: print ('Spam')
answer = input('Press y to end this loop')
if answer == 'y':
print ('Fries with that?')
break
print ('Have a ')
print ('nice day!')
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11. The continue statement
05-06.py
while 1:
print ('Spam')
answer = input('Press y for large fries ')
if answer == 'y':
print ('Large fries with spam, mmmm, yummy ')
continue
answer = input('Had enough yet? ')
break
print ('Have a ')
print ('nice day!')
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12. A Sentinel-Controlled while loop
05-07.py
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13. Python Repetition and String Formatting
The while loop
The for loop
String formatting
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14. Counter-controlled repetition with the for loop
for c in range (10):
print (c)
05-08.py
This program prints the numbers 0 through 9.
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15. Counter-controlled repetition with the for loop
for c in range (5,10):
print (c)
05-09.py
This program prints the numbers 5 through 9.
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16. Using continue with the for loop
for c in range (1,6):
if c == 3:
continue
print (c)
05-10.py
This program prints the numbers 1, 2, 4, 5, (skips 3).
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17. Using break with the for loop
for c in range (1,6):
if c == 3:
break
print (c)
05-11.py
This program prints the numbers 1 and 2.
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18. Python Repetition and String Formatting
The while loop
The for loop
String formatting
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19. Printing strings and numbers
We can print string values and number values from the same print statement by separating them with commas:
d = 10
c = 75
print ('Total is: ', d, 'dollars and', c, ' cents ')
>>>
Total is: 10 dollars and 75 cents
05-12.py
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20. Numbers can be printed from within a single string by using a special method known as string formatting.
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21. String Formatting and %
In string formatting, we use the % symbol. The % operator can also be used for a different purpose as the modulus operator (finding the remainder after an integer division). The % symbol is said to be overloaded.
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22. String Formatting and %
An overloaded operator behaves differently depending on the context. In the following example we see the % operator being used to specify how a string should be printed (i.e. string formatting).
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23. Printing integers within a string
x = 20
y = 75
print ('The sum of %d and %d is %d' % (x, y, x + y))
>>>
The sum of 20 and 75 is 95
The three %d formatting codes represent where the decimal integers shown in brackets after the % symbol should be printed.
05-13.py
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24. Printing floats within a string
x =
y =
print ('The sum of %f and %f is %f' % (x, y, x + y))
>>>
The sum of and is
The three %f represent where the float values shown in brackets after the % symbol should be printed.
05-13.py
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25. Specifying the number of decimal places
x =
y =
print ('The sum of %0.2f and %0.2f is %0.2f' % (x, y, x + y))
>>>
The sum of and is 35.78
The three %0.2f represent where the float values (to 2 decimal places) shown in brackets after the % symbol should be printed.
05-13.py
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26. String formatting codes
%d and %f are only two of a set of formatting codes available for string formatting.
See:
for more details.
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27. Repeating a progam at the user’s request
print ("This is the start of the program")
answer = 'y'
while (answer == 'y' or answer == 'Y'):
print ("This is a statement from within the while loop")
print ("This is another statement from within the while loop")
answer = input("Do you want to run this program again? y/n")
print ("Goodbye! ")
05-14.py
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28. Loops within loops - nested loops
for i in range (1,6):
for j in range (1,6):
print ("i: " + str(i) + " j: " + str(j) )
print()
'''
Notice that with a loop repeating 5 times,
***within*** a loop that repeats 5 times
means that you can control 25 processes. py
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29. This presentation uses the following program files:
05-01.py
05-02.py
05-03.py
05-04.py
05-05.py
05-06.py
05-07.py
05-08.py
05-09.py
05-10.py
05-11.py
05-12.py
05-13.py
05-14.py
05-15.py
05-16.py
05-17.py
05-18.py
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30. End of Python_Repetition_StringFormatting.ppt
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31. Last updated: Sunday 24th May 2009, 15:58 PT, AHD
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AHD c 2010