1. Aleksandar Kuzmanovic Northwestern University
EECS 110: Lec 3: Data
Aleksandar Kuzmanovic
Northwestern University

2. What is computer science (CS)?
CS != programming
What is computer science (CS)?
Take EECS 101

3. What is computer science (CS)?
CS != programming
What is computer science (CS)?
Take EECS 101
"not equal to"

4. a vehicle, not a destination
CS != programming
programming : CS ::
machining : engineering
grammar : literature
Programming
equations : mathematics CS
a vehicle, not a destination

5. Programming as learning a foreign language
What is programming?
Programming as learning a foreign language
1) Expect it to be different!
2) Don’t feel you need to memorize it
3) Immersion == Experimentation

6. The foreign language of Python…
syntax?
semantics?
intent?
How it looks
What it does
What it should do
name = input('Hi... what is your name? ')
print # prints a blank line
if name == ’Ning': # is it Ning?
print( name, '??’)
print(‘You must be a TA!')
elif name == ‘Aleksandar’: # is it Aleksandar?
print( ‘You must be an instructor!')
else: # in all other cases...
print( 'Welcome to Python,', name, '!')

7. The foreign language of Python…
syntax?
semantics?
intent?
How it looks
What it does
What it should do
name = input('Hi... what is your name? ')
print # prints a blank line
if name == ’Ning': # is it Ning?
print( name, '??’)
print(‘You must be a TA!')
elif name == ‘Aleksandar’: # is it Aleksandar?
print( ‘You must be an instructor!')
else: # in all other cases...
print( 'Welcome to Python,', name, '!')

8. The foreign language of Python
syntax?
semantics?
intent?
How it looks
What it does
What it should do
how punctuation is used
the language keywords that are used
use of whitespace
peculiarities of formatting
how behavior is affected …

9. Goal: Thinking like a machine
Today
Data!
Labs at Wilkinson Lab
tomorrow:
Half of Homework 1
Bring your laptop if you’d like
Goal: Thinking like a machine

10. “Kinds” of data
What examples of data can you think of?

11. “Kinds” of data What examples of data can you think of? Video
Statistics
Binary (I/0, True/False)
Matrices
Qualitative/quantitative

12. What will these results be?
Python (numeric) data types
What will these results be?
Dominant
float
1 / 5
long
10** **100
int
1 // 5
0.2 42
bool
41 + True
Recessive

13. Python Operators Precedence Caution Level = ( ) / ** % * % / ** + - ==
set equal to
Highest /
divide **
Python Operators %
remainder * % / **
power + -
is equal to ==
>
< == * =
Lowest +
>
as usual
<
It's not worth remembering all these %+/* things! -
I’d go with parentheses over precedence
( )

14. % the “mod” operator 7 % 3 8 % 3 9 % 3 16 % 7 x%2 == 0
x%y returns the remainder when x is divided by y
7 % 3
8 % 3
9 % 3
16 % 7
x%2 == 0
For what values of x are these True?
x%2 == 1
x%4 == 0
What happens on these years?

15. Naming data
>> x = 41
>> y = x + 1

16. Inside the machine… x = 41 y = x + 1 41 42 Computation Data Storage
What's happening in python:
x = 41
y = x + 1
What is happening behind the scenes:
"variables as containers" 41 42
name: x
type: int
LOC: 300
name: y
type: int
LOC: 304
memory location 300
memory location 304
Computation
Data Storage
id, del

17. is a long list of memory locations
Computer memory
Random Access Memory (RAM)
is a long list of memory locations
on or off
bit = 1 "bucket" of charge
byte = 8 bits
word = 4 bytes = 32 bits 42
name: x
type: int
LOC: 300
4 bytes for an int

18. Naming data >> x = 41 >> y = x + 1 >> x 4142
>> x = x + y ??

19. Naming data >> x = 41 >> y = x + 1 >> x 4142
>> x = x + y
?? 83 ??

20. Naming data >> x = 41 >> y = x + 1 >> x 4142
>> x = x + y
?? 83
?? 42

21. You need lists of numbers, as well!
Are numbers enough?
No!
You need lists of numbers, as well!
list
and strings are helpful, too.
str

22. Can all this information be represented using lists ?
More complex data
{ 2, 3, 5, 7, 11 }
‘Many years later, as he faced the firing squad, Colonel Aureliano Buendia was to remember that distant afternoon when his father took him to discover ice.’
Text
Sets
Can all this information be represented using lists ?
Sounds/Speech
Networks
Images/Video
Ideas?

23. string functions str len + * s1 = 'ha' Given these strings s2 = 't'
str(42) returns '42'
converts input to a string
len('42') returns 2
returns the string’s length
'XL' + 'II' returns 'XLII'
concatenates strings
'VI'*7 returns 'VIVIVIVIVIVIVI'
repeats strings
s1 = 'ha'
Given these strings
s2 = 't'
‘hat’
‘hahathathat’
What are
s1 + s2
2*s1 + s2 + 2*(s1+s2)

24. s = 'northwestern university'
String surgery
s = 'northwestern university' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
s[ ]
indexes into the string, returning a one-character string
index
s[0] returns 'n'
Read "s-of-zero" or "s-zero"
s[12]returns
S[ ] returns 'h'
Which index returns 'e'?
s[len(s)] returns
python != English

25. s = 'northwestern university'
String surgery
s = 'northwestern university' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
s[ ]
indexes into the string, returning a one-character string
index
s[0] returns 'n'
Read "s-of-zero" or "s-zero"
s[12]returns ' '
S[ ] returns 'h'
Which index returns 'e'?
s[len(s)] returns
python != English

26. s = 'northwestern university'
String surgery
s = 'northwestern university' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
s[ ]
indexes into the string, returning a one-character string
index
s[0] returns 'n'
Read "s-of-zero" or "s-zero"
s[12]returns ' '
S[4] returns 'h'
Which index returns 'e'?
s[len(s)] returns
python != English

27. s = 'northwestern university'
String surgery
s = 'northwestern university' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
s[ ]
indexes into the string, returning a one-character string
index
s[0] returns 'n'
Read "s-of-zero" or "s-zero"
s[12]returns ' '
S[4] returns 'h'
Which index returns 'e'?
s[len(s)] returns ERROR
python != English

28. s = 'northwestern university'
Negative indices… 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
s = 'northwestern university'
-23
-21
-19
-17
-15
-13
-11 -9 -7 -5 -3 -1
-22
-20
-18
-16
-14
-12
-10 -8 -6 -4 -2
Negative indices count backwards from the end!
s[-1] returns 'y'
S[-11] = ‘ ‘
S[-0] = n
s[-11] returns
s[-0] returns

29. s = 'northwestern university'
Slicing
s = 'northwestern university' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
s[ : ]
slices the string, returning a substring
What's going on here?
s[0:5] returns 'north'
s[5:9] returns 'west'
s[17:] returns 'ersity'
s[:] returns 'northwestern university'

30. s = 'northwestern university'
Slicing
s = 'northwestern university' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
s[ : ]
slices the string, returning a substring
the first index is the first character of the slice
the second index is ONE AFTER the last character
a missing index means the end of the string
s[0:5] returns 'north'
s[5:9] returns 'west'
s[17:] returns 'ersity'
s[:] returns 'northwestern university'

31. s = 'northwestern university'
Skip-slicing
s = 'northwestern university' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
s[ : : ]
skip-slices, returning a subsequence
the third index is the "stride" length
it defaults to 1
s[0:8:2] returns 'nrhe'
'ruv'
What skip-slice returns
What does this return?
s[1::6]

32. s = 'northwestern university'
Skip-slicing
s = 'northwestern university' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
s[ : : ]
skip-slices, returning a subsequence
the third index is the "stride" length
it defaults to 1
s[0:8:2] returns 'nrhe'
'ruv' s[10:17:3]
What skip-slice returns
What does this return?
s[1::6]

33. s = 'northwestern university'
Skip-slicing
s = 'northwestern university' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
s[ : : ]
skip-slices, returning a subsequence
the third index is the "stride" length
it defaults to 1
s[0:8:2] returns 'nrhe'
'ruv' s[10:17:3]
What skip-slice returns
What does this return?
s[1::6] 'osus'

34. Lists ~ Strings of anything
Commas separate elements.
Lists ~ Strings of anything
L = [ 3.14, [2,40], 'third', 42 ]
Square brackets tell python you want a list.
len(L)
L[0]
Indexing: could return a different type
Slicing: always returns the same type
L[0:1]
How could you extract from L
'hi'

35. Lists ~ Strings of anything
Commas separate elements.
Lists ~ Strings of anything
L = [ 3.14, [2,40], 'third', 42 ]
Square brackets tell python you want a list.
len(L) 4
L[0]
Indexing: could return a different type
Slicing: always returns the same type
L[0:1]
How could you extract from L
'hi'

36. Lists ~ Strings of anything
Commas separate elements.
Lists ~ Strings of anything
L = [ 3.14, [2,40], 'third', 42 ]
Square brackets tell python you want a list.
len(L) 4
L[0] 3.14
Indexing: could return a different type
Slicing: always returns the same type
L[0:1]
How could you extract from L
'hi'

37. Lists ~ Strings of anything
Commas separate elements.
Lists ~ Strings of anything
L = [ 3.14, [2,40], 'third', 42 ]
Square brackets tell python you want a list.
len(L) 4
L[0] 3.14
Indexing: could return a different type
Slicing: always returns the same type
L[0:1] [3.14]
How could you extract from L
'hi'

38. Lists ~ Strings of anything
Commas separate elements.
Lists ~ Strings of anything
L = [ 3.14, [2,40], 'third', 42 ]
Square brackets tell python you want a list.
len(L) 4
L[0] 3.14
Indexing: could return a different type
Slicing: always returns the same type
L[0:1] [3.14]
How could you extract from L
'hi' L[2][1:3]

39. message = 'You need parentheses for chemistry !'
"Quiz"
Raising and razing lists
Name(s):
pi = [3,1,4,1,5,9]
Q = [ 'pi', "isn't", [4,2] ]
message = 'You need parentheses for chemistry !'
Part 1
Part 2
len(pi)
Q[0]
What are
len(Q)
Q[0:1]
len(Q[1])
What are
Q[0][1]
Q[1][0]
What slice of pi is [3,1,4]
What slice of pi is [3,4,5]
What is message[9:15]
What are
pi[0] * (pi[1] + pi[2])
and
pi[0] * (pi[1:2] + pi[2:3])
What is message[::5]
Extra! Mind Muddlers
What is pi[pi[2]]?
How many nested pi's before pi[…pi[0]…] produces an error?

40. message = 'You need parentheses for chemistry !'
"Quiz"
Raising and razing lists
Name(s):
pi = [3,1,4,1,5,9]
Q = [ 'pi', "isn't", [4,2] ]
message = 'You need parentheses for chemistry !'
Part 1
Part 2
len(pi)
Q[0]
What are
len(Q)
Q[0:1]
len(Q[1])
What are
Q[0][1]
Q[1][0]
What slice of pi is [3,1,4]
What slice of pi is [3,4,5]
What is message[9:15]
What are
pi[0] * (pi[1] + pi[2])
and
pi[0] * (pi[1:2] + pi[2:3])
What is message[::5]
Extra! Mind Muddlers
What is pi[pi[2]]?
How many nested pi's before pi[…pi[0]…] produces an error?