In programming, data type is an important concept.
Variables can store data of different types, and different types can do different things.
Python has the following data types built-in by default, in these categories:
Text Type: str
Numeric Types: int, float, complex
Sequence Types: list, tuple, range
Mapping Type: dict
Set Types: set, frozenset
Boolean Type: bool
Binary Types: bytes, bytearray, memoryview
Like many other popular programming languages, strings in Python are arrays of bytes representing unicode characters.
However, Python does not have a character data type, a single character is simply a string with a length of 1.
Square brackets can be used to access elements of the string.
# Get the character at position 1 (remember that the first character has the position 0):
a = "Hello, World!"
print(a[1])
Output:
e
You can return a range of characters by using the slice syntax.
Specify the start index and the end index, separated by a colon, to return a part of the string.
# Get the characters from position 2 to position 5 (not included):
b = "Hello, World!"
print(b[2:5])
Output:
llo
Use negative indexes to start the slice from the end of the string:
# Get the characters from position 5 to position 1, starting the count from the end of the string:
b = "Hello, World!"
print(b[-5:-2])
Output:
orl
To get the length of a string, use the len() function.
# The len() function returns the length of a string:
a = "Hello, World!"
print(len(a))
Output:
13
Python has a set of built-in methods that you can use on strings.
# The strip() method removes any whitespace from the beginning or the end:
a = " Hello, World! "
print(a.strip()) # returns "Hello, World!"
Output:
Hello, World!
# The lower() method returns the string in lower case:
a = "Hello, World!"
print(a.lower())
Output:
hello, world!
# The upper() method returns the string in upper case:
a = "Hello, World!"
print(a.upper())
Output:
HELLO, WORLD!
# The replace() method replaces a string with another string:
a = "Hello, World!"
print(a.replace("H", "J"))
Output:
Jello, World!
# The split() method splits the string into substrings if it finds instances of the separator:
a = "Hello, World!"
print(a.split(","))
Output:
['Hello', ' World!']
There may be times when you want to specify a type on to a variable. This can be done with casting. Python is an object-orientated language, and as such it uses classes to define data types, including its primitive types.
Casting in python is therefore done using constructor functions:
int() - constructs an integer number from an integer literal, a float literal (by rounding down to the previous whole number), or a string literal (providing the string represents a whole number)float() - constructs a float number from an integer literal, a float literal or a string literal (providing the string represents a float or an integer)str() - constructs a string from a wide variety of data types, including strings, integer literals and float literalsx = int(1) # x will be 1
y = int(2.8) # y will be 2
z = int("3") # z will be 3