Common data types in Python

Numeric data type
Boolean data type
String data type
Nothing data type
Wrapping up

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

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"'
```

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
  s = 'id,name,address'
  res = s.split(',')

  # result: ['id', 'address', 'name']
```
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(',')

  # result: ('id', ',', 'address,name')
```
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.

Table of contents

Numeric data type

Boolean data type

String data type

Nothing data type

Wrapping up