Basic Strings (Python From Zero To One — Part 18)

Day 88 of experimenting with video content

Intro to Strings

a = 'hello world'
b = "apple pie"

We can think of strings as a sequence of characters, and we use either single or double quotes (both works) to define strings. Here, a is a string, and b is also a string.

String addition & multiplication

a = 'apple'
b = 'pie'

print(a + b)  # applepie
print(b + a)  # pieapple

^ adding strings joins them together (order matters)

a = 'apple'

print(a * 3)  # appleappleapple

^ multiplying a string with an integer n joins n of the string together.

Note — a string can only be added with another string, and a string can only be multiplied with an integer. We get errors if we try anything else.

Compound assignment operators

a = 'apple'
a += 'pie'

print(a)    # applepie

^ a += 'pie' means we add 'pie' to the back of a

a = 'apple'
a *= 3

print(a)    # appleappleapple

^ a *= 3 means we multiply a by 3

Basic indexing

string = 'abcde'

print(string[0])    # a
print(string[1])    # b
print(string[2])    # c
print(string[3])    # d
print(string[4])    # e

When we index a string eg. string[n] where n is an integer, we are actually getting the character at that certain index n.

In Python, we start counting from 0, so the index of our first character a would be 0.

• index of a in abcde is 0
• index of b in abcde is 1
• index of c in abcde is 2
• index of d in abcde is 3
• index of e in abcde is 4

Index out of range error

string = 'abcde'

print(string[0])    # a
print(string[1])    # b
print(string[2])    # c
print(string[3])    # d
print(string[4])    # e

print(string[5])    # index out of range error

if we attempt to index a character that isn’t there, we get an index out of range error. Here in the string abcde, we only have characters up til index 4 (5th position) — if we try to index 5, we just get an error.

Negative indexes

string = 'abcde'

print(string[-1])    # e
print(string[-2])    # d
print(string[-3])    # c
print(string[-4])    # b
print(string[-5])    # a

When we pass in negative indexes when doing string indexing, we start counting from the right instead of the usual left side.

• e is at index -1
• d is at index -2
• c is at index -3
• b is at index -4
• a is at index -5

Which can be useful if we are dealing with characters nearer to the right end of our string.

string = 'abcde'

print(string[-1])    # e
print(string[-2])    # d
print(string[-3])    # c
print(string[-4])    # b
print(string[-5])    # a

print(string[-6])    # index out of range error

^ similarly, if we attempt to use a negative index that doesn’t exist in the string, we will just get an index out of range error.

Conclusion

Hope this was clear and easy to understand.

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