## Numeric data type

Python has three number data types:

• integer data type
• real data type
• float data type

## Boolean data type

Values of boolean data types are: True and False.

For example:

``````male = True
female = False
x = 5 > 9
``````

## String data type

1. Some ways to create string

In Python, there are three ways of the string’s creation:

• Using the third double quotes

``````  tmp = """Hello
world
"""
``````
• Using single quote

``````  tmp = 'Hello world'
``````
• Using double quotes

``````  tmp = "Hi"
``````

In order to use the quotes in a string, there are some ways:

• Using \ character

``````  tmp = 'Hello, \"world\"'
``````
• Mixing some types of quotes

``````  tmp = 'Hello "world"'
``````
2. Some useful methods

• Get the length of a string

``````  tmp = 'Hello world'
print(len(tmp))
``````
• trim spaces in a string

Using strip(), rstrip(), lstrip() methods to remove the redendancy spaces. These methods will return a new string that contains our results.

``````  s = ' Hello world  '
s1 = s.rstrip()
s2 = s.lstrip()
s3 = s.strip()
``````
• compare two string

Using some operators: ==, !=, … that returns boolean data type.

``````  s = 'Hello world'
s1 = 'hello World'
print(s == s1)
``````
• access an item in a string

When using index’s value is negative, it means that we will iterate from the last string.

``````  s = 'Hello world'
s1 = s[0:10]    # s1 = 'Hello worl'
s2 = s[:]       # s2 = 'Hello world'
s3 = s[-2]      # s3 = 'w'
``````
• Search substring in a string

Using find(), rfind(), index(), rindex() methods.

• rfind(), rindex() methods will search from the last string.
• find(), index() methods search from the beginning string.

With find() method, if it doesn’t find a substring, it will return -1. However, the index() method will throw an exception ValueError if not found a substring.

For example:

``````  s = 'Hello world'
try:
print(s.index('Hello'))
except ValueError as ex:
print(ex)
``````
• Operator on a string

* operator is used to multiply a string to x times.

``````  s = 'Hello world'
print(s * 2)

# result: Hello worldHello world
``````

+ operator is used to concate multiple strings

``````  print('Hello' + 'world')
``````

In Java, C++, string and number data types can be implicitly combined to a string. However, Python does not allow this way, we need to cast data types explicitly by using int(), str(), float() methods.

``````  print('Hello world' + 2)    # cannot concate with int
print('Hello world' + str(2))
``````
• Split, combine strings

To split a string, using split(), rsplit() methods. Its result is a list of strings that is seperated from the original string.

``````  # csv file
res = s.split(',')

``````

There is another way to split a string, using partition() method - only split at the first time when it copes with a seperated character. Its result is always a list of three elements. The first element is a segment of string that is before the seperated character, and the next element is the seperated character, the final element is a segment of string that lies after the seperated character.

``````  s = 'id,name,address'
res = s.partition(',')

``````
• Format string

Some symbols for for string: %d, %x, %#x (adde 0x to string), %o, %e.

``````  print('Hello world %d' % 2)
print('Hello %f %s' % (2.5 'world'))
``````
• Useful methods

Methods Meaning
upper() convert all characters in a string to upper case
lower() convert all characters in a string to lower case
swapcase() lowercase –> uppercase, uppercase –> lowercase
title() convert first character to uppercase, the remained characters to lowercase
isalpha() check whether a character is a letter or not
isdigit() check whether a character is a number or not
ljust()
rjust()

## Nothing data type

Using None value.

``````s = None
``````

## Wrapping up

• Understanding the common data types, especially the string data type.