Based on Zed Shaw's "Learn Python the Hard Way," this is a review of Exercises 1 - 12 in that text. For non-computer-science students and learners. Updated with new slides Jan. 12, 2014. Introduces math, print statement, variables, format strings, raw_input().

1. Learn Python the Hard Way
Exercises 1 – 12
http://learnpythonthehardway.org/

2. Exercise 1: Quotation marks
Which of these will throw an error?
a)
b)
c)
d)
print "They wouldn't do that."
print 'They wouldn't do that.'
print 'They wouldn't do that.'
print "They wouldn't do that.'

3. Exercise 2: Comments
Which line is commented out?
a) print "Fourscore and seven years"
b) # print "Fourscore"
c) print "Eighty years" # this is fourscore years

4. Which one will print blank lines?
1) print "Fourscore and seven years ago"
#
#
print "Our fathers brought forth"
2) print "Fourscore and seven years ago"
print
print
print "Our fathers brought forth"

5. Exercise 3: Math
Which one of these would give a different
answer than the others?
a)
b)
c)
d)
e)
4+6/3+5
4 + (6 / 3) + 5
(4 + 6) / 3 + 5
(4 + 6 / 3) + 5
4 + (6 / 3 + 5)

6. PEMDAS
•
•
•
•
•
•
P
E
M
D
A
S
()
exponents, e.g. 10**2
*
/
+
–
But …

7. PEMDAS is not the whole story
•P ()
• E exponents, e.g. 10**2
• MD * / %
• AS + –
See http://en.wikipedia.org/wiki/Order_of_operations

8. Exercise 4: Math
What is the answer Python will give to all of
these?
a)
b)
c)
d)
5 > 10
10 < 2
1444 < 1443
1>2

9. Exercise 4: Math
True or False:
<
>
<=
>=
==
!=
More about True and False to come, in Zed’s
exercise 27.
(Note: In Python, these values always start with
an uppercase letter.)

10. Exercise 5: Integers and floats
What is the answer Python will give to this?
1/4

11. Exercise 5: Integers and floats
What is the answer Python will give to this?
1 / 4.0

12. Learn this!
>>> 1 / 4
0
>>>
>>> 1 / 4.0
0.25
>>>
integer
float

14. Exercise 6: Modulus
What is the answer Python will give to all of
these?
a)
b)
c)
d)
4%2
10 % 2
144 % 12
100 % 25

15. Modulo
The modulus operand is commonly used to find out if a
number is odd or even.
%
Don’t get confused: In Python, the percent sign (yes,
the same character, but used differently) is also used
for format strings, as seen first in Exercise 5. (You’ll be
seeing even more of that!)

16. Modulo (also modulus)
What will this return?
(That is, what answer will Python give?)
115 % 11

17. Variables

18. Variables
Name
apple
Value

19. Variables

20. Variables

22. Variables
Name
Value

23. Variables
Name
Value

24. Variables
Name
Value
57

25. Variables
Name
Value

26. Any questions?

27. “Format strings”
• %s %d %r %f
• Each one is slightly different
• They are a kind of shorthand for working with
variables in Python
• NOTE! These are NOT variables!
• Zed also calls these “format characters”
• NOTE! This is NOT modulus!

28. %r %s %d
Not all the same.

29. Notice how %r in this case returns
something very different from %s

30. String formatting continued
•
•
•
•
%s string: use this for text
%d use this for integers (no decimal places)
%f float: shows up to 6 decimal places
%r representation: works for numbers and
strings, but (usually) adds quotation marks *
* Zed says, “The %r is best for debugging.”
(But you don’t really know what debugging is.)

31. The value of “play”
(an essential part of learning to code)

32. n newline (line break)
t tab (indent)
The backslash is
“the escape character.”

33. Putting things together
a = "Mary had a little lamb."
b = "Its fleece was white as snow."
c = "And everywhere that Mary went"
d = "The lamb was sure to go."
print "nn%snt%sn%snt%snn" % (a, b, c, d)
What would happen if the order were changed to: (d, c, b, a)

35. Running that program …

36. Escapes
Zed says memorize all of these. I don’t think
that’s necessary.
But do memorize this:
The backslash is the escape character.

37. Escapes!

38. raw_input( )
Zed’s exercises 11 and 12 introduce this.

39. raw_input( )

40. Learn Python the Hard Way
Exercises 1 – 12
(we’re just getting started)