message = 'HELLO WORLD'
print(message)10 Strings
The string datatype represents textual messages, comprised of any number of alphanumeric characters.
10.1 Characteristics
There are three ways to construct a string: by using single quotes, double quotes, or a multi-line string.
Single quotes (') on the extremities:
Double quotes (") on the extremities:
message = "HELLO WORLD"
print(message)Multiline string, uses triple quotes (""") on the extremities:
message = """
This is a menu for our application.
To get started, follow these instructions:
1. __________
2. ____________
3. _____________
"""
print(message)In practice, we might prefer to use double quotes by default. This allows us to use single quotes inside for contractions, whereas this would otherwise break the quoting level:
message = "It's awesome!"
print(message)#message = 'It's awesome!' # NOT VALID (BREAKS QUOTING LEVEL)
#print(message)10.2 Operations
In practice, some common operations we perform with strings include concatenation, case manipulation, and substring checking, among others.
10.2.1 Concatenation
message = "HELLO" + "WORLD"
print(message)
message = "HELLO " + "WORLD"
print(message)
message = "HELLO" + " WORLD"
print(message)
message = "HELLO" + " " + "WORLD"
print(message)10.2.2 Format Strings
As an alternative to concatenation, we can use a format string to dynamically compile a string.
Recall that we are not able to concatenate strings with non-string datatypes such as numbers. To overcome this limitation, we could use string conversion function, or more commonly, a format string.
The format string allows us to inject one or more variables into a string.
To implement a format string, we need the letter f immediately preceding the string. And we need curly braces ({}) inside the string. This allows us to inject a variable inside the curly braces:
price = 4.5
print(f"PRICE: ${price}")We can use a formatting directive such as :.2f to format a number to two decimal places, for example to format a number as US Dollars (USD):
price = 4.5
print(f"PRICE: ${price:.2f}")A formatting directive such as :, to use a thousands separator:
shares = 120000
print(f"SHARES: {shares:,}")Notice, it is possible to inject multiple variables in the format string, and to mix and match formatting directives:
price = 4.5
shares = 120000
stake = price * shares
print(f"PRICE: ${price:.2f} | SHARES: {shares:,} | STAKE: ${stake:,.2f}")10.2.3 Case Manipulation
Converting to all uppercase:
"hello WorlD".upper()Converting to all lowercase:
"hello WorlD".lower()Converting to title case, where the first letter of each word is capitalized:
"hello WorlD".title()10.2.4 Substring Checking
We can use the inclusion operator to perform substring checking:
"h" in "hello world"Note this is case sensitive:
"H" in "hello world"10.2.5 Substring Replacement
It is possible to replace all instances of a substring within a larger string:
"hello world. as the world turns.".replace("world", "globe")10.2.6 Length Checking
A string is like a list of individual characters.
Like a list, we can use the len function to count the number of characters in a string:
len("HELLO WORLD")10.2.7 String Indexing and Slicing
Similar to list operations, we can use indices to reference a specific character in the string, or a sequence of characters (i.e. string slicing):
"HELLO WORLD"[0]"HELLO WORLD"[0:5]10.2.8 String Splitting
The split method will split a string on a designated delimiter:
"hello world".split(" ")"first | second | third".split(" | ")