Table of contents

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
    • 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'
    • 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'
        except ValueError as 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

Nothing data type

Using None value.

s = None

Wrapping up

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