Python Numbers
There are three numeric types in Python:
intfloatcomplex
Variables of numeric types are created when you assign a value to them:
Example
x = 1 # int
y = 2.8 # float
z = 1j # complex
To verify the type of any object in Python, use the type() function:
Example
print(type(x))
print(type(y))
print(type(z))
Int
Int, or integer, is a whole number, positive or negative, without decimals, of unlimited length.
Example
Integers:
x = 1
y = 35656222554887711
z = -3255522
print(type(x))
print(type(y))
print(type(z))Float
Float, or "floating point number" is a number, positive or negative, containing one or more decimals.
Example
Floats:
x = 1.10
y = 1.0
z = -35.59
print(type(x))
print(type(y))
print(type(z))Float can also be scientific numbers with an "e" to indicate the power of 10.
Example
Floats:
x = 35e3
y = 12E4
z = -87.7e100
print(type(x))
print(type(y))
print(type(z))Complex
Complex numbers are written with a "j" as the imaginary part:
Example
Complex:
x = 3+5j
y = 5j
z = -5j
print(type(x))
print(type(y))
print(type(z))Type Conversion
You can convert from one type to another with the int(), float(), and complex() methods:
Example
Convert from one type to another:
x = 1 # int
y = 2.8 # float
z = 1j # complex
#convert from int to float:
a = float(x)
#convert from float to int:
b = int(y)
#convert from int to complex:
c = complex(x)
print(a)
print(b)
print(c)
print(type(a))
print(type(b))
print(type(c))Note: You cannot convert complex numbers into another number type.
Random Number
Python does not have a random() function to make a random number, but Python has a built-in module called random that can be used to make random numbers:
Example
Import the random module, and display a random number between 1 and 9:
import random
print(random.randrange(1, 10))Python Casting
Specify a Variable Type
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 removing all decimals), 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 literals
Example
Integers:
x = int(1) # x will be 1
y = int(2.8) # y will be 2
z = int("3") # z will be 3
Example
Floats:
x = float(1) # x will be 1.0
y = float(2.8) # y will be 2.8
z = float("3") # z will be 3.0
w = float("4.2") # w will be 4.2
Example
Strings:
x = str("s1") # x will be 's1'
y = str(2) # y will be '2'
z = str(3.0) # z will be '3.0'Strings
Strings in python are surrounded by either single quotation marks, or double quotation marks.
'hello' is the same as "hello".
You can display a string literal with the print() function:
Example
print("Hello")
print('Hello')Assign String to a Variable
Assigning a string to a variable is done with the variable name followed by an equal sign and the string:
Example
a = "Hello"
print(a)Multiline Strings
You can assign a multiline string to a variable by using three quotes:
Example
You can use three double quotes:
a = """Lorem ipsum dolor sit amet,
consectetur adipiscing elit,
sed do eiusmod tempor incididunt
ut labore et dolore magna aliqua."""
print(a)Or three single quotes:
Example
a = '''Lorem ipsum dolor sit amet,
consectetur adipiscing elit,
sed do eiusmod tempor incididunt
ut labore et dolore magna aliqua.'''
print(a)Note: in the result, the line breaks are inserted at the same position as in the code.
Strings are Arrays
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.
Example
Get the character at position 1 (remember that the first character has the position 0):
a = "Hello, World!"
print(a[1])Looping Through a String
Since strings are arrays, we can loop through the characters in a string, with a for loop.
Example
Loop through the letters in the word "banana":
for x in "banana":
print(x)Learn more about For Loops in our Python For Loops chapter.
String Length
To get the length of a string, use the len() function.
Example
The len() function returns the length of a string:
a = "Hello, World!"
print(len(a))Check String
To check if a certain phrase or character is present in a string, we can use the keyword in.
Example
Check if "free" is present in the following text:
txt = "The best things in life are free!"
print("free" in txt)
Use it in an if statement:
Example
Print only if "free" is present:
txt = "The best things in life are free!"
if "free" in txt:
print("Yes, 'free' is present.")Learn more about If statements in our Python If...Else chapter.
Check if NOT
To check if a certain phrase or character is NOT present in a string, we can use the keyword not in.
Example
Check if "expensive" is NOT present in the following text:
txt = "The best things in life are free!"
print("expensive" not in txt)Use it in an if statement:
Example
print only if "expensive" is NOT present:
txt = "The best things in life are free!"
if "expensive" not in txt:
print("No, 'expensive' is NOT present.")Slicing
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.
Example
Get the characters from position 2 to position 5 (not included):
b = "Hello, World!"
print(b[2:5])Note: The first character has index 0.
Slice From the Start
By leaving out the start index, the range will start at the first character:
Example
Get the characters from the start to position 5 (not included):
b = "Hello, World!"
print(b[:5])Slice To the End
By leaving out the end index, the range will go to the end:
Example
Get the characters from position 2, and all the way to the end:
b = "Hello, World!"
print(b[2:])Negative Indexing
Use negative indexes to start the slice from the end of the string:Example
Get the characters:
From: "o" in "World!" (position -5)
To, but not included: "d" in "World!" (position -2):
b = "Hello, World!"
print(b[-5:-2])Python has a set of built-in methods that you can use on strings.
Upper Case
Example
The upper() method returns the string in upper case:
a = "Hello, World!"
print(a.upper())Lower Case
Example
The lower() method returns the string in lower case:
a = "Hello, World!"
print(a.lower())Remove Whitespace
Whitespace is the space before and/or after the actual text, and very often you want to remove this space.
Example
The strip() method removes any whitespace from the beginning or the end:
a = " Hello, World! "
print(a.strip()) # returns "Hello, World!"Replace String
Example
The replace() method replaces a string with another string:
a = "Hello, World!"
print(a.replace("H", "J"))Split String
The split() method returns a list where the text between the specified separator becomes the list items.
Example
The split() method splits the string into substrings if it finds instances of the separator:
a = "Hello, World!"
print(a.split(",")) # returns ['Hello', ' World!']String Concatenation
To concatenate, or combine, two strings you can use the + operator.
Example
Merge variable a with variable b into variable c:
a = "Hello"
b = "World"
c = a + b
print(c)Example
To add a space between them, add a " ":
a = "Hello"
b = "World"
c = a + " " + b
print(c)String Format
As we learned in the Python Variables chapter, we cannot combine strings and numbers like this:
Example
age = 36
txt = "My name is John, I am " + age
print(txt)But we can combine strings and numbers by using the format() method!
The format() method takes the passed arguments, formats them, and places them in the string where the placeholders {} are:
Example
Use the format() method to insert numbers into strings:
age = 36
txt = "My name is John, and I am {}"
print(txt.format(age))The format() method takes unlimited number of arguments, and are placed into the respective placeholders:
Example
quantity = 3
itemno = 567
price = 49.95
myorder = "I want {} pieces of item {} for {} dollars."
print(myorder.format(quantity, itemno, price))You can use index numbers {0} to be sure the arguments are placed in the correct placeholders:
Example
quantity = 3
itemno = 567
price = 49.95
myorder = "I want to pay {2} dollars for {0} pieces of item {1}."
print(myorder.format(quantity, itemno, price))Escape Character
To insert characters that are illegal in a string, use an escape character.
An escape character is a backslash \ followed by the character you want to insert.
An example of an illegal character is a double quote inside a string that is surrounded by double quotes:
Example
You will get an error if you use double quotes inside a string that is surrounded by double quotes:
txt = "We are the so-called "Vikings" from the north."To fix this problem, use the escape character \":
Example
The escape character allows you to use double quotes when you normally would not be allowed:
txt = "We are the so-called \"Vikings\" from the north."Escape Characters
Other escape characters used in Python:
| Code | Result | Try it |
|---|---|---|
| \' | Single Quote | |
| \\ | Backslash | |
| \n | New Line | |
| \r | Carriage Return | |
| \t | Tab | |
| \b | Backspace | |
| \f | Form Feed | |
| \ooo | Octal value | |
| \xhh | Hex value |
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