[8] Text I: Strings and Their Slices

---

[8.2] Strings, Indexing, Slicing

string - a sequence of characters, indicated with surrounding quotation marks—either single or double, as long as both starting and ending quotation marks are the same. They are not numbers.

'' = null string

len('hello world')

11

len('')

0

hi = 'hello world'

len(hi)

11

print(hi)

hello world

len("hello world")

11

heyno = "Hello, but can't come" #with double quotes we can have a single quote inside a string

print(heyno)

Hello, but can't come

'hello, can't do it' #cannot have single quote inside a string this way

  File "/tmp/ipykernel_9389/3416001661.py", line 1
    'hello, can't do it' #cannot have single quote inside a string this way
                ^
SyntaxError: invalid syntax

len(2112) #“integers don’t have a length in Python”

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
/tmp/ipykernel_9389/1965248679.py in <module>
----> 1 len(2112) #“integers don’t have a length in Python”

TypeError: object of type 'int' has no len()

len('1312')

4

index - the character's index is its position in the string;

Character number zero is the character that is zero away from the beginning of the string - the first one

'hello'[0]

'h'

'hello'[1]

'e'

'hello'[2]

'l'

'hello'[3]

'l'

'hello'[4]

'o'

'hello'[5]

---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
/tmp/ipykernel_9389/2204331286.py in <module>
----> 1 'hello'[5]

IndexError: string index out of range

[8.3] Selecting a Slice

'hello world'[0:3]

'hel'

'2112'[0:3]

'211'

''[0:3]

''

'hello'[0:1]

'h'

'hello'[0]

'h'

''[0:1]

''

''[0]

---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
/tmp/ipykernel_9389/1334571462.py in <module>
----> 1 ''[0]

IndexError: string index out of range

'hello'[0:500]

'hello'

'hello'[450:500]

''

hey = 'hello world'

hey[:3]

'hel'

hey[1:]

'ello world'

ell = hey[1:4]

ell

'ell'

greeting = 'hello world'

greeting[0].upper() + greeting[1:]

'Hello world'

'abcdefgh'[0:9:2]

'aceg'

'hello world'[0:10:2]

'hlowr'

'hello world'[0:11:3]

'hlwl'

'hello world'[0:]

'hello world'

'abcdefgh'[::2]

'aceg'

'0123456789'[::2] #even numbers

'02468'

'0123456789'[::4]

'048'

hey[-1]

'd'

hey[-1:] #the last character

'd'

hey[-5] # the 5th characters backwards

'w'

hey[-5:] # the last 5 characters in the string

'world'

[8.4] Counting Double Letters

wyatt = 'They flee from me that sometime did me seek / With naked foot, stalking in my chamber.' 

'HELLO World'.lower()

'hello world'

original = 'Burma Shave'

lowercase = original.lower()

lowercase

'burma shave'

original

'Burma Shave'

wyatt = wyatt.lower() #overwriting the original string with lower cases

wyatt

'they flee from me that sometime did me seek / with naked foot, stalking in my chamber.'

iterating through wyatt and simply find all the occurrences of a double 'e':

#1. iterate through the string:

for c in wyatt:
    print(c)

t
h
e
y
 
f
l
e
e
 
f
r
o
m
 
m
e
 
t
h
a
t
 
s
o
m
e
t
i
m
e
 
d
i
d
 
m
e
 
s
e
e
k
 
/
 
w
i
t
h
 
n
a
k
e
d
 
f
o
o
t
,
 
s
t
a
l
k
i
n
g
 
i
n
 
m
y
 
c
h
a
m
b
e
r
.

for i in range(len(wyatt)):
    print(wyatt[i])

t
h
e
y
 
f
l
e
e
 
f
r
o
m
 
m
e
 
t
h
a
t
 
s
o
m
e
t
i
m
e
 
d
i
d
 
m
e
 
s
e
e
k
 
/
 
w
i
t
h
 
n
a
k
e
d
 
f
o
o
t
,
 
s
t
a
l
k
i
n
g
 
i
n
 
m
y
 
c
h
a
m
b
e
r
.

for i in range(len(wyatt)):
    print(i, wyatt[i]) #adding the index position before each index - [i]

0 t
1 h
2 e
3 y
4  
5 f
6 l
7 e
8 e
9  
10 f
11 r
12 o
13 m
14  
15 m
16 e
17  
18 t
19 h
20 a
21 t
22  
23 s
24 o
25 m
26 e
27 t
28 i
29 m
30 e
31  
32 d
33 i
34 d
35  
36 m
37 e
38  
39 s
40 e
41 e
42 k
43  
44 /
45  
46 w
47 i
48 t
49 h
50  
51 n
52 a
53 k
54 e
55 d
56  
57 f
58 o
59 o
60 t
61 ,
62  
63 s
64 t
65 a
66 l
67 k
68 i
69 n
70 g
71  
72 i
73 n
74  
75 m
76 y
77  
78 c
79 h
80 a
81 m
82 b
83 e
84 r
85 .

i

85

list(range(len(wyatt)))

[0,
 1,
 2,
 3,
 4,
 5,
 6,
 7,
 8,
 9,
 10,
 11,
 12,
 13,
 14,
 15,
 16,
 17,
 18,
 19,
 20,
 21,
 22,
 23,
 24,
 25,
 26,
 27,
 28,
 29,
 30,
 31,
 32,
 33,
 34,
 35,
 36,
 37,
 38,
 39,
 40,
 41,
 42,
 43,
 44,
 45,
 46,
 47,
 48,
 49,
 50,
 51,
 52,
 53,
 54,
 55,
 56,
 57,
 58,
 59,
 60,
 61,
 62,
 63,
 64,
 65,
 66,
 67,
 68,
 69,
 70,
 71,
 72,
 73,
 74,
 75,
 76,
 77,
 78,
 79,
 80,
 81,
 82,
 83,
 84,
 85]

len(wyatt)

86

wyatt[i]

'.'

for i in range(len(wyatt)):
    print (wyatt[i:i+2])
    
    #identifying each pair of letters

th
he
ey
y 
 f
fl
le
ee
e 
 f
fr
ro
om
m 
 m
me
e 
 t
th
ha
at
t 
 s
so
om
me
et
ti
im
me
e 
 d
di
id
d 
 m
me
e 
 s
se
ee
ek
k 
 /
/ 
 w
wi
it
th
h 
 n
na
ak
ke
ed
d 
 f
fo
oo
ot
t,
, 
 s
st
ta
al
lk
ki
in
ng
g 
 i
in
n 
 m
my
y 
 c
ch
ha
am
mb
be
er
r.
.

pairs = 0
for i in range(len(wyatt)):
    if wyatt[i:i+2] == 'ee':
        pairs = pairs + 1

pairs

2

pairs = 0
for i in range(len(wyatt)):
    if wyatt[i] == wyatt[i+1]:
        pairs = pairs + 1

---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
/tmp/ipykernel_9389/3701685584.py in <module>
      1 pairs = 0
      2 for i in range(len(wyatt)):
----> 3     if wyatt[i] == wyatt[i+1]:
      4         pairs = pairs + 1

IndexError: string index out of range

pairs

3

wyatt[86]

---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
/tmp/ipykernel_9389/3230828111.py in <module>
----> 1 wyatt[86]

IndexError: string index out of range

pairs = 0
for i in range(len(wyatt)-1):
    if wyatt[i] == wyatt[i+1]:
        pairs = pairs + 1

pairs

3

print(pairs)

3

Exe. 8-1

def twin(text):
    text = text.lower()
    pairs = 0
    for i in range(len(text) - 1):
        if text[i] == text[i + 1]:
            pairs = pairs + 1
    return(pairs)
        

twin(wyatt)

3

twin('Hello world')

1

twin('Alex')

0

[8.5] Strings and Their Length

text = 'All human beings are born free and equal in dignity and rights. They are endowed with reason and conscience and should act towards one another in a spirit of brotherhood.'

text

'All human beings are born free and equal in dignity and rights. They are endowed with reason and conscience and should act towards one another in a spirit of brotherhood.'

len(text)

170

[8.6] Splitting a Text into Words: First Attempt

split(), divides a string into a list of strings, breaking it apart whenever the specified string (the one given as an argument) is found

text.split(' ')

['All',
 'human',
 'beings',
 'are',
 'born',
 'free',
 'and',
 'equal',
 'in',
 'dignity',
 'and',
 'rights.',
 'They',
 'are',
 'endowed',
 'with',
 'reason',
 'and',
 'conscience',
 'and',
 'should',
 'act',
 'towards',
 'one',
 'another',
 'in',
 'a',
 'spirit',
 'of',
 'brotherhood.']

text

'All human beings are born free and equal in dignity and rights. They are endowed with reason and conscience and should act towards one another in a spirit of brotherhood.'

len(text.split(' ')) #checking len of the split text

30

text.split('and')

['All human beings are born free ',
 ' equal in dignity ',
 ' rights. They are endowed with reason ',
 ' conscience ',
 ' should act towards one another in a spirit of brotherhood.']

text.split('in') #uses the argument for splitting

['All human be',
 'gs are born free and equal ',
 ' dignity and rights. They are endowed with reason and conscience and should act towards one another ',
 ' a spirit of brotherhood.']

hi = 'hello   world'
hi.split(' ')

['hello', '', '', 'world']

'hello   world'.split(' ')

['hello', '', '', 'world']

text.split() # uses any sequence of whitespace

['All',
 'human',
 'beings',
 'are',
 'born',
 'free',
 'and',
 'equal',
 'in',
 'dignity',
 'and',
 'rights.',
 'They',
 'are',
 'endowed',
 'with',
 'reason',
 'and',
 'conscience',
 'and',
 'should',
 'act',
 'towards',
 'one',
 'another',
 'in',
 'a',
 'spirit',
 'of',
 'brotherhood.']

hi.split()

['hello', 'world']

[8.7] Working across Strings: Joining, Sorting

names = ['Bob', 'Carol', 'Ted', 'Alice']

' & '.join(names)

'Bob & Carol & Ted & Alice'

join - a method of the string that is used to do the joining; it is not a method of the list

names.join(' & ') #a list doesn't have a join attribute

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
/tmp/ipykernel_9389/3595420381.py in <module>
----> 1 names.join(' & ') #a list doesn't have a join attribute

AttributeError: 'list' object has no attribute 'join'

names

['Bob', 'Carol', 'Ted', 'Alice']

' & '.join(names)

'Bob & Carol & Ted & Alice'

' and/or '.join(names)

'Bob and/or Carol and/or Ted and/or Alice'

'\n'.join(names)

'Bob\nCarol\nTed\nAlice'

print('\n'.join(names)) #printing list as a string in a column with new line

Bob
Carol
Ted
Alice

print(' exists.\n'.join(names)) # element "exists" is just before the new line

Bob exists.
Carol exists.
Ted exists.
Alice

print((' has left.\n'.join(names)) + ' is here.')

Bob has left.
Carol has left.
Ted has left.
Alice is here.

[8.8] Each Word without Joining

for person in names:
    print(person + ' exists.') # iterating in each element in the list "names"

Bob exists.
Carol exists.
Ted exists.
Alice exists.

def naming(string):
    for person in ('\n'.join(names)):
        if person[-1] == 'l':
            return (person + ' exists.')
        else:
            return (person + ' has left.')

naming(names)

'B has left.'

names

['Bob', 'Carol', 'Ted', 'Alice']

sorted(names) #alphabetically sorted sequence

['Alice', 'Bob', 'Carol', 'Ted']

names

['Bob', 'Carol', 'Ted', 'Alice']

namesorder = names.sort()

namesorder

names.sort()

names

['Alice', 'Bob', 'Carol', 'Ted']

[Exercise 8-2] Same Last Character

Write same_last(), a function that accepts two strings as arguments and returns True if they have the same last letter, False otherwise.

def same_last(name1, name2):
    if name1[-1] == name2[-1]:
        return True
    else:
        return False

same_last('Maria', 'Gloria')

True

[Exercise 8-3] Counting Spaces

Write count_spaces(), a function that accepts a string as an argument and returns the number of spaces in the string. Use iteration to determine this.

def count_spaces(text):
    count = 0
    for i in range(len(text) - 1):
        if text[i] == ' ':
            count = count + 1
    return(count)

count_spaces(names)

0

new = ('Welcome in the new metaverse')

count_spaces(new)

4

[Exercise 8-4] Counting Nonspaces

Write count_nonspaces(), a function that returns the number of characters in a string that are not spaces.

def count_nonspaces(text):
    count = 0
    for i in range(len(text) - 1):
        if text[i] == ' ':
            count = count
        else:
            count = count + 1
    return(count)

count_nonspaces(new)

23

len(new)

28

28-4

24