Lesson 02-03: Substrings with String Slicing¶

Substrings¶

We can use string indexing to get a single character from a string. Sometimes, though, we will want to get multiple letters, maybe a part of a string. Any “string within a string” is called a substring.

For example, the "pizza" contains the substrings:

"piz"
"iz"
"izza"
"zz"

and so on (there’s more)!

String Slicing Notation¶

To get a substring from a string, we still use string indexing, but this time, instead of giving a single number in the [] brackets, we give a range - two numbers, separated by a colon. The syntax for string slicing is as follows:

some_string[a:b]

Where:

• some_string is the original string
• a is the index of where to begin slicing (includes this index)
• b is the index of where to end slicing (excludes this index)

Let’s look at some examples:

phrase = "pants are cool"

# index:  0123456789 123

print("\n\n") #ignore this line

print(phrase[0:4])

print(phrase[6:8])

print(phrase[10:13])

print()

print(phrase[3:7])

print(phrase[2:3])

​

pant
ar
coo

ts a
n

(ex_strslice_1)

The important thing to remember when slicing strings is that The range goes up to but does not include the second number.

Special Python Syntax¶

Similar to how python has negative indexes, it also has some tricks for quick slicing. You don’t need to know this, but it might be helpful.

Special Syntax	Meaning
[:x]	The first x letters
[:-x]	Everything except the last x letters
[x:]	Everything except the first x letters
[-x:]	The last x letters

Check For Understanding¶