1. Line Continuation, Output Formatting, and Decision Structures
COSC 1301

2. Line Continuation
What do you do if your line of Python code is too long?
Use the line continuation character!
the backslash character \
Place at the very end of the line
Python interpreter will assume the next line is part of the same line
Saw in Camus.py
Show in interpreter

3. Line Continuation: Example
>>> sum = \ \ 25 >>> sum >>> print (“\t\nHello, my name is”, \ “Jarvis”) Hello, my name is Jarvis

4. Output Formatting We’ve seen this:
print (“The temperature is”,temp,”degrees”)
Now, we’ll see another way
Better able to control how print displays values
> 88.33
4 / 15 / > 4/15/2010

5. Output Formatting: Format Operators
print (“The temperature is %d degrees” % temp)
String formatting operator: %
NOT modulus: modulus operates on numbers
Appears in strings
Indicates how and where a value should be printed in a string
Also indicates end of print string and beginning of the values to be printed

6. Output Formatting: Format Operators
print (“The temperature is %d degrees” % temp)
Indicates the type and format of the value
Indicates the end of the string to be printed and the beginning of the values specified in the string

7. Output Formatting: Format Specifiers
Value Type %d
integer %f
float %s
string
%e or %E
exponential
For each, you can also specify width and precision:
%<width>.<precision><type character>
print (“The average is %3.2f” % avg)
What about long?
Precision mostly comes into play for floats, where it specifies places after the decimal place---rounds!
but can be used for integers, where it pads with 0s
Width is the total number of spaces the field should occupy
Example: math.pi
Modify average.py

8. Output Formatting: Embedded Operations
You can calculate values in your print statement: print (“2+3 = %d” % (2+3)) print (“x/y = %.2f” % (x/y))
Do in IDLE

9. Formatting Example >>> import math # package containing pi
>>> math.pi #display the value of pi
>>> #Now display with 4 digits after decimal point
>>> print (“Pi: %.4f” % math.pi)
Pi:
Notes:
The f in the format string stands for float.
The number appears in the output wherever the format string occurs.
The number is rounded to the specified number of digits.

10. Formatting Example
Can specify a minimum field width for the display of a value
Minimum width comes before the decimal point in the format string
>>> print (“Pi: %7.3f” % math.pi)
Pi:
The field width is 7:
digits and decimal point: width 5
2 blank spaces to left of number

11. Formatting: Two or More Values
Enclose multiple values in parentheses
Separate the values with commas
print (“First name: %10s, Last Name: %12s” % (“Elvis”, “Presley”))
First name: Elvis, Last Name: Presley

12. Output Formatting: Examples
Modify average.py to print 2 decimal places of the average
Practice printing strings from input()
Print using multiple values
The values must be enclosed in parentheses

13. Question for you: Output Formatting
What is the expected output? x = 5.7 y = 2.18 print (“%.1f” % (x+y)) A. 7 C. 7.9 B. 7.8 D. 8 C

14. Comparisons Allows you to compare two values
Result in a True or False value
type Boolean (bool)
You can compare numbers or strings, literals, variables, or expressions
Where have you seen this before?

15. How do you specify a comparison?
Specify the condition using a relational operator
Operator
Meaning
<
Less than
>
Greater than
<=
Less than or equal
>=
Greater than or equal ==
Equality !=
Not equals

16. Comparisons: Examples
test = 13 < 15
test = 101 >= 99
test = “a” < “b”
test = 4 == 2+2
test = 15 != 16
test = 12 == 3*5

17. Lexicographic Order Strings are rated according to lexicographic order
Orders words A-Za-z
Capital letters first in alphabetical order
Lower-case letters second in alphabetical order
NOT in dictionary order

18. Decisions “Once you make a decision, the universe conspires to make it happen.” -- Ralph Waldo Emerson
Gives you the ability to specify different instructions based on a condition
The condition is typically a comparison
if some comparison is true:
do something
Where have you seen this before?

19. Decisions: if Statement
def main(): command if(<condition>): main()
Commands not dependent on the condition
Commands only executed if condition is true
Indentation matters! (Again)
Parentheses are optional in Python
Do not want to duplicate code---you’ll have to correct mistakes twice
The commands executed only if it is true is called the body or block of the if statement.
But what if we also want commands executed if it is false?...
Extend Average to say, “You passed!”

20. if examples
number = 25 if number > 10: print (number, “is greater than 10!”) Output: 25 is greater than 10!

21. Decisions: if-else Statement
if(<condition>): command else:
Commands only executed if condition is True
Extend average to say “You failed!”
Commands only executed if condition is False

22. if-else exercise
Write a program that asks the user to enter a number. If the number is 3, print a message indicating that they entered your favorite number, and otherwise, indicate that you don’t like the chosen number.

23. Decisions: if-elif-else Statement
if(<condition>): command elif(<condition>): else:
Commands only executed if condition is True
You can used as many of these as you like
Commands only executed if earlier conditions are False and this condition is True
Elif is a contraction for else-if
Extend average to say “You got a perfect score!”
You can also nest the conditionals
Commands only executed if EVERY condition is False

24. if-elif-else example
number = int(input(“Please enter your number: “)) if number < 10: print number, “is small” elif number < 100: print number, “is pretty big” elif number < 500: print number, “is big” else: print “Wow, a really big number!” Sample Run: Please enter your number: is big

25. Decisions: Nested ifs
You can put if statements inside the body of the if (or elif or else) statement:
if(<condition>):
if(<some other condition>):
command
else:
elif(<condition>): …
Grade example: if-elif… : Print "A", "B", …, "F"
Then nest if-else in body of first block: if grade >= 97, print "A+", else print "A".

26. Decisions: Gotchas
Exactly ONE of the bodies in if-elif-else will be executed
Only the first True condition
THINK about the construction of your if statements before coding
Comparison of floats
if(.3 == .1+.2) is False

27. Question for you: Decisions
What is the expected output? if(125<140): print “first one” elif(156>=140): print (“second one”) else: print(“third one”) A. first one C. third one B. second one D. first one second one