Download presentation
Presentation is loading. Please wait.
Published byKenneth McCoy Modified over 8 years ago
1
EECS 110: Lec 3: Data Aleksandar Kuzmanovic Northwestern University http://networks.cs.northwestern.edu/EECS110-s15/
2
CS != programming What is computer science (CS)? Take EECS 101
3
CS != programming What is computer science (CS)? Take EECS 101 "not equal to"
4
4 Programming CS a vehicle, not a destination programming : CS :: machining : engineering grammar : literature equations : mathematics CS != programming
5
What is programming? 5 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… 6 syntax? How it looks semantics? What it does intent? 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… 7 syntax? How it looks semantics? What it does intent? 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 8 syntax? How it looks semantics? What it does intent? 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
9 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? 10
11
“Kinds” of data What examples of data can you think of? –Video –Statistics –Binary (I/0, True/False) –Matrices –Qualitative/quantitative 11
12
bool Dominant int long float Recessive 41 + True 10**100 - 10**100 1 / 5 1 // 5 What will these results be? Python (numeric) data types
13
Python Operators I’d go with parentheses over precedence Precedence * % ** / > < == + - Caution Level = Highest Lowest ** *%/><==+- = ( ) It's not worth remembering all these %+/* things! remainder power is equal to set equal to divide as usual
14
7 % 3 8 % 3 9 % 3 16 % 7 x%4 == 0 x%2 == 0 For what values of x are these True ? What happens on these years? x%y returns the remainder when x is divided by y x%2 == 1 % the “mod” operator
15
>> x = 41 >> y = x + 1 Naming data
16
x = 41 y = x + 1 name: x type: int LOC: 300 41 What is happening behind the scenes: What's happening in python: "variables as containers" memory location 300 id, del ComputationData Storage name: y type: int LOC: 304 42 memory location 304 Inside the machine…
17
Random Access Memory (RAM) byte = 8 bits word = 4 bytes = 32 bits is a long list of memory locations bit = 1 "bucket" of charge name: x type: int LOC: 300 4 bytes for an int on or off 42 Computer memory
18
>> x = 41 >> y = x + 1 >> x 41 >> y 42 >> x = x + y >> x ?? >> y ?? Naming data
19
>> x = 41 >> y = x + 1 >> x 41 >> y 42 >> x = x + y >> x ?? 83 >> y ?? Naming data
20
>> x = 41 >> y = x + 1 >> x 41 >> y 42 >> x = x + y >> x ?? 83 >> y ?? 42 Naming data
21
Are numbers enough? No! You need lists of numbers, as well! and strings are helpful, too. list str
22
Networks Images/Video Sounds/Speech { 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 Ideas? Can all this information be represented using lists ? More complex data
23
str ing functions str len + * converts input to a string returns the string’s length str(42) returns '42' len('42') returns 2 'XL' + 'II' returns 'XLII' 'VI'*7 returns 'VIVIVIVIVIVIVI' concatenates strings repeats strings s1 = 'ha' s2 = 't' Given these strings s1 + s2 2*s1 + s2 + 2*(s1+s2) What are
24
s[ ] indexes into the string, returning a one-character string s = 'northwestern university' s[0] returns 'n' s[12] returns 0123456789 101112131415161718 S[ ] returns 'h' Which index returns 'e'? python != English s[len(s)] returns Read "s-of-zero" or "s-zero" index String surgery 19 2021 22
25
s[ ] indexes into the string, returning a one-character string s = 'northwestern university' s[0] returns 'n' s[12] returns ' ' 0123456789 101112131415161718 S[ ] returns 'h' Which index returns 'e'? python != English s[len(s)] returns Read "s-of-zero" or "s-zero" index String surgery 19 2021 22
26
s[ ] indexes into the string, returning a one-character string s = 'northwestern university' s[0] returns 'n' s[12] returns ' ' 0123456789 101112131415161718 S[4] returns 'h' Which index returns 'e'? python != English s[len(s)] returns Read "s-of-zero" or "s-zero" index String surgery 19 2021 22
27
s[ ] indexes into the string, returning a one-character string s = 'northwestern university' s[0] returns 'n' s[12] returns ' ' 0123456789 101112131415161718 S[4] returns 'h' Which index returns 'e'? python != English s[len(s)] returnsERROR Read "s-of-zero" or "s-zero" index String surgery 19 2021 22
28
s = 'northwestern university' Negative indices… -2 -3 -4 -5 -6 -7 -8 -9 -10 -11 -12 -13 -14 -15 -16 -17 -18 -19 0123456789 10111213141516171819 2021 22 -20 -21 -22 -23 Negative indices count backwards from the end! s[-1] returns 'y' s[-11] returns s[-0] returns
29
s[ : ] slices the string, returning a substring s[5:9] returns 'west' s[0:5] returns 'north' What's going on here? s[17:] returns 'ersity' s[:] returns 'northwestern university' Slicing s = 'northwestern university' 0123456789 10111213141516171819 2021 22
30
s[ : ] slices the string, returning a substring s[5:9] returns 'west' s[0:5] returns 'north' s[17:] returns 'ersity' s[:] returns 'northwestern university' Slicing s = 'northwestern university' 0123456789 10111213141516171819 2021 22 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
31
Skip-slicing s = 'northwestern university' 0123456789 10111213141516171819 2021 22 s[ : : ] skip-slices, returning a subsequence the third index is the "stride" length it defaults to 1 s[0:8:2] returns 'nrhe' What skip-slice returns What does this return? 'ruv' s[1::6]
32
Skip-slicing s = 'northwestern university' 0123456789 10111213141516171819 2021 22 s[ : : ] skip-slices, returning a subsequence the third index is the "stride" length it defaults to 1 s[0:8:2] returns 'nrhe' What skip-slice returns What does this return? 'ruv' s[10:17:3] s[1::6]
33
Skip-slicing s = 'northwestern university' 0123456789 10111213141516171819 2021 22 s[ : : ] skip-slices, returning a subsequence the third index is the "stride" length it defaults to 1 s[0:8:2] returns 'nrhe' What skip-slice returns What does this return? 'ruv' s[10:17:3] s[1::6] 'osus'
34
Lists ~ Strings of anything L = [ 3.14, [2,40], 'third', 42 ] Square brackets tell python you want a list. len(L) L[0] L[0:1] 'hi' How could you extract from L Slicing: always returns the same type Indexing: could return a different type Commas separate elements.
35
Lists ~ Strings of anything L = [ 3.14, [2,40], 'third', 42 ] Square brackets tell python you want a list. len(L)4 L[0] L[0:1] 'hi' How could you extract from L Slicing: always returns the same type Indexing: could return a different type Commas separate elements.
36
Lists ~ Strings of anything L = [ 3.14, [2,40], 'third', 42 ] Square brackets tell python you want a list. L[0]3.14 L[0:1] 'hi' How could you extract from L Slicing: always returns the same type Indexing: could return a different type Commas separate elements. len(L)4
37
Lists ~ Strings of anything L = [ 3.14, [2,40], 'third', 42 ] Square brackets tell python you want a list. L[0]3.14 L[0:1][3.14] 'hi' How could you extract from L Slicing: always returns the same type Indexing: could return a different type Commas separate elements. len(L)4
38
Lists ~ Strings of anything L = [ 3.14, [2,40], 'third', 42 ] Square brackets tell python you want a list. L[0]3.14 L[0:1][3.14] 'hi' L[2][1:3] How could you extract from L Slicing: always returns the same type Indexing: could return a different type Commas separate elements. len(L)4
39
Raising and razing lists What are "Quiz" pi = [3,1,4,1,5,9]Q = [ 'pi', "isn't", [4,2] ] What slice of pi is [3,4,5] What is pi[pi[2]] ? message = 'You need parentheses for chemistry !' What is message[::5] What are pi[0] * (pi[1] + pi[2]) and pi[0] * (pi[1:2] + pi[2:3]) What is message[9:15] What are What slice of pi is [3,1,4] How many nested pi 's before pi[…pi[0]…] produces an error? Name(s): Extra! Mind Muddlers Part 2Part 1 Q[0] Q[0:1] Q[0][1] Q[1][0] len(pi) len(Q) len(Q[1])
40
Raising and razing lists What are "Quiz" pi = [3,1,4,1,5,9]Q = [ 'pi', "isn't", [4,2] ] What slice of pi is [3,4,5] What is pi[pi[2]] ? message = 'You need parentheses for chemistry !' What is message[::5] What are pi[0] * (pi[1] + pi[2]) and pi[0] * (pi[1:2] + pi[2:3]) What is message[9:15] What are What slice of pi is [3,1,4] How many nested pi 's before pi[…pi[0]…] produces an error? Name(s): Extra! Mind Muddlers Part 2Part 1 Q[0] Q[0:1] Q[0][1] Q[1][0] len(pi) len(Q) len(Q[1])
41
If statements (1) 41 name = input('Hi... what is your name? ') if name == ’Ning': # is it Ning? print('x1’) else: # in all other cases... print('x2’) print('x3’)
42
If statements (2) 42 name = input('Hi... what is your name? ') if name == ’Ning‘: print('x1’) else: print('x2’) print('x3’)
43
If statements (3) 43 name = input('Hi... what is your name? ') if name == ’Ning': print( 'x1' ) elif name == 'Aleksandar': print( 'x2' ) else: print( 'x3’ ) print( 'x4’ )
44
If statements (4) 44 name = input('Hi... what is your name? ') if name == ’Ning': print( 'x1' ) elif name == 'Aleksandar': print( 'x2' ) else: print( 'x3’ ) print( 'x4’ )
45
If statements (5) 45 name = input('Hi... what is your name? ') if name == ’Ning': # is it Ning? print( 'x1' ) elif name == 'Aleksandar': print( 'x2' ) elif name == 'Lisa': print( 'x3' ) else: # in all other cases... print( 'x4’ ) print( 'x5’ )
46
If statements (6) 46 name = input('Hi... what is your name? ') if name == ’Ning‘: print( 'x1’ ) elif name == 'Aleksandar’: print( 'x2' ) elif name == 'Lisa': print( 'x3' ) else: print( 'x4’ ) print( 'x5’ )
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.