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programming

Strings. Indexing. Slices

1.

NIS PhM Kostanay
Strings. Indexing. Slices
Unit Unit 11.2А: Data structure.
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Learning objectives:
• 11.2.2.3 apply functions and string
processing methods;
• 11.2.2.1 perform access to the elements of
strings, lists, tuples;
• 11.2.2.2 use slicers to process the string;
• 11.2.3.6 determine the difference between
different data structures.
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3.

How to create string?
fixed_word = 'Programming'
print(fixed_word)
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4.

How to create string?
fixed_word = 'Programming'
print(fixed_word)
word = input()
print(word)
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5.

How to create string?
fixed_word = 'Programming'
print(fixed_word)
word = input()
print(word)
number = 25
number_string = str(number)
print(number_string)
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6.

How to create string?
fixed_word = 'Programming'
print(fixed_word)
word = input()
print(word)
number = 25
number_string = str(number)
print(number_string)
word_plus_number = fixed_word +
number_string
print(word_plus_number)
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7.

Strings
• A string is a sequence of characters.
• You can access individual characters in a string using an index in square brackets. The string
indexing starts from 0.
• You can also access a string by negative indexing. A negative string index counts from the
end of the string.
• The indices for the elements in a string are illustrated as below:
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8.

Access Characters by Index
• # Indexing
• S = 'ABCDEFGHI'
• print(S[0])
# Prints A
• print(S[4])
# Prints E
• # Negative Indexing
• S = 'ABCDEFGHI'
• print(S[-1])
# Prints I
• print(S[-6])
# Prints D
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9.

String Concatenation
# concatenation operator
S = 'Hello,' + ' World!'
print(S)
# Hello, World!
# augmented assignment operator
S = 'Hello,'
S += ' World!'
print(S)
# Hello, World!
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10.

Find String Length
S = 'Supercalifragilisticexpialidocious'
print(len(S))
# Prints 34
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11.

Iterate Through a String
To iterate over the characters of a string, use a simple
for loop.
# Print each character in a string
S = 'Hello, World!'
for letter in S:
print(letter, end=' ')
#Hello, World!
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12.

Iterate Through an Indexes
To iterate over the indexes of a string, use a simple
for loop.
# Print each character in a string
S = 'Hello, World!'
for i in range(len(S)):
print(S[i], end=' ')
#Hello, World!
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13.

Task. Count vowels in string.
Use set:
text = 'Hello, my dear friends!'
vowels = 0
for letter in text:
if letter in {'a', 'e', 'i', 'o', 'u', 'y’}:
vowels += 1
print(vowels)
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14.

Task. Count vowels in string.
Use string:
text = 'Hello, my dear friends!'
vowels = 0
for i in range(len(text)):
if text[i] in 'aeiouy’:
vowels += 1
print(vowels)
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15.

Slicing a String
A segment of a string is called a slice and you can extract one by using a slice operator. A slice of a
string is also a string.
The slice operator [n:m] returns the part of the string from the “n-th” item to the “m-th” item,
including the first but excluding the last.
S = 'ABCDEFGHI’
print(S[2:5])
print(S[5:-1])
print(S[1:6:2])
# Prints CDE
# Prints FGH
# Prints BDF
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16.

String slices
text = 'Hello, world!'
0
1
2
3
4
5
H e
l
l
o
,
6
7
8
9
10
11
12
w o
r
l
d
!
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17.

String slices
text = 'Hello, world!'
0
1
2
3
4
5
H
e
l
l
o
,
6
7
8
9
10
11
12
w
o
r
l
d
!
print(text[0:5])
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18.

String slices
text = 'Hello, world!'
0
1
2
3
4
5
H
e
l
l
o
,
print(text[0:5])
6
7
8
9
10
11
12
w
o
r
l
d
!
Hello
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19.

String slices
text = 'Hello, world!'
0
1
2
3
4
5
H
e
l
l
o
,
print(text[0:5])
print(text[7:12])
6
7
8
9
10
11
12
w
o
r
l
d
!
Hello
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20.

String slices
text = 'Hello, world!'
0
1
2
3
4
5
H
e
l
l
o
,
print(text[0:5])
print(text[7:12])
6
7
8
9
10
11
12
w
o
r
l
d
!
Hello
world
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21.

String slices
text = 'Hello, world!'
0
1
2
3
4
5
H
e
l
l
o
,
print(text[0:5])
print(text[7:12])
print(text[:5])
6
7
8
9
10
11
12
w
o
r
l
d
!
Hello
world
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22.

String slices
text = 'Hello, world!'
0
1
2
3
4
5
H
e
l
l
o
,
print(text[0:5])
print(text[7:12])
print(text[:5])
6
7
8
9
10
11
12
w
o
r
l
d
!
Hello
world
Hello
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23.

String slices
text = 'Hello, world!'
0
1
2
3
4
5
H
e
l
l
o
,
print(text[0:5])
print(text[7:12])
print(text[:5])
6
7
8
9
10
11
12
w
o
r
l
d
!
Hello
world
Hello
print(text[7:])
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24.

String slices
text = 'Hello, world!'
0
1
2
3
4
5
H
e
l
l
o
,
print(text[0:5])
print(text[7:12])
print(text[:5])
print(text[7:])
6
7
8
9
10
11
12
w
o
r
l
d
!
Hello
world
Hello
world!
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25.

String slices
text = 'Hello, world!'
0
1
2
3
4
5
H
e
l
l
o
,
print(text[0:5])
print(text[7:12])
print(text[:5])
print(text[7:])
print(text[:])
6
7
8
9
10
11
12
w
o
r
l
d
!
Hello
world
Hello
world!
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26.

27.

String slices
text = 'Hello, world!'
0
1
2
3
4
5
H
e
l
l
o
,
print(text[0:5])
print(text[7:12])
print(text[:5])
print(text[7:])
print(text[:])
print(text[11:15])
6
7
8
9
10
11
12
w
o
r
l
d
!
Hello
world
Hello
world!
Hello, world!
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28.

29.

String slices
text = 'Hello, world!'
0
1
2
3
4
5
H
e
l
l
o
,
-13
-12
-11
-10
-9
-8
6
-7
7
8
9
10
11
12
w
o
r
l
d
!
-6
-5
-4
-3
-2
-1
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30.

String slices
text = 'Hello, world!'
0
1
2
3
4
5
H
e
l
l
o
,
-13
-12
-11
-10
-9
-8
6
-7
7
8
9
10
11
12
w
o
r
l
d
!
-6
-5
-4
-3
-2
-1
print(text[:-9])
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31.

String slices
text = 'Hello, world!'
0
1
2
3
4
5
H
e
l
l
o
,
-13
-12
-11
-10
-9
-8
print(text[:-9])
6
-7
7
8
9
10
11
12
w
o
r
l
d
!
-6
-5
-4
-3
-2
-1
Hell
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32.

String slices
text = 'Hello, world!'
0
1
2
3
4
5
H
e
l
l
o
,
-13
-12
-11
-10
-9
-8
print(text[:-9])
print(text[-5:-3])
6
-7
7
8
9
10
11
12
w
o
r
l
d
!
-6
-5
-4
-3
-2
-1
Hell
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33.

String slices
text = 'Hello, world!'
0
1
2
3
4
5
H
e
l
l
o
,
-13
-12
-11
-10
-9
-8
print(text[:-9])
print(text[-5:-3])
6
-7
7
8
9
10
11
12
w
o
r
l
d
!
-6
-5
-4
-3
-2
-1
Hell
or
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34.

String slices
text = 'Hello, world!'
0
1
2
3
4
5
H
e
l
l
o
,
-13
-12
-11
-10
-9
-8
print(text[:-9])
print(text[-5:-3])
print(text[-6:])
6
-7
7
8
9
10
11
12
w
o
r
l
d
!
-6
-5
-4
-3
-2
-1
Hell
or
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35.

String slices
text = 'Hello, world!'
0
1
2
3
4
5
H
e
l
l
o
,
-13
-12
-11
-10
-9
-8
print(text[:-9])
print(text[-5:-3])
print(text[-6:])
6
-7
7
8
9
10
11
12
w
o
r
l
d
!
-6
-5
-4
-3
-2
-1
Hell
or
world!
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36.

37.

String slices
text = 'Hello, world!'
0
1
2
3
4
5
H
e
l
l
o
,
-13
-12
-11
-10
-9
-8
print(text[:-9])
print(text[-5:-3])
print(text[-6:])
print(text[:1])
6
-7
7
8
9
10
11
12
w
o
r
l
d
!
-6
-5
-4
-3
-2
-1
Hell
or
world!
H
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38.

39.

String slices
text = 'Hello, world!'
0
1
2
3
4
5
H
e
l
l
o
,
-13
-12
-11
-10
-9
-8
print(text[:-9])
print(text[-5:-3])
print(text[-6:])
print(text[:1])
print(text[-1:])
6
-7
7
8
9
10
11
12
w
o
r
l
d
!
-6
-5
-4
-3
-2
-1
Hell
or
world!
H
!
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