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.
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.
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')
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'))
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
- Understanding the common data types, especially the string data type.