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This article focuses on "how to understand Python numbers and strings". Interested friends may wish to have a look at it. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn how to understand Python numbers and strings.

01 digit

The number types of Python3 can be divided into integer type, floating point type, Boolean type, fraction type and plural type. When writing a program in Python, you do not need to declare the type of the variable. The variables are managed by the basic data types built in Python, and the operations such as the association of values and types and type conversion are realized in the background of the program.

Python is quite different from other high-level languages in the way and internal principles of defining variables. In C or Java, define an integer variable, which can be expressed as follows:

Int I = 1

In Python, the expression of defining integer variables is more concise.

I = 1

Python automatically determines the type of variable according to the value of the variable, programmers do not need to care about what type the variable is, as long as they know that a number is stored in the created variable, and the future work is only to operate on this value, and Python will be responsible for the life cycle of this number.

More importantly, C or Java simply creates an int-type normal variable; Python creates an integer object, and Python automatically creates the integer object, which no longer needs to be created through a constructor. There are no normal types within Python, and any type is an object. If C or Java needs to change the value of variable I, just reassign it; Python cannot change the value of object I. For example:

The two I below are not the same object "2i = 1" 3print (id (I)) "4i = 2" 5print (id (I))

If you need to see the type of variable, you can use the type class defined by Python. Type is a class of the _ _ builtin__ module that can return the type of a variable or create a new type. The _ _ builtin__ module is the inline module of Python. The inline module does not require import statements and is automatically imported by the Python interpreter. You will be exposed to more inline module classes and functions later.

The following code returns the types of various variables.

"integer" 2i = 1 "3print (type (I))" long integer "5l = 99999999999999999999990 # Python when to convert int to float related to operating system digits" 6print type (l) "floating point" 8f = 1.2 "9 print (type (f)" 1 "Boolean" 11b = True "12print (type (b)

[code description]

Line 3 outputs the result:

Line 6 outputs the result:

Line 9 outputs the result:

Line 12 outputs the result:

It is also convenient to use Python for scientific calculations because Python has built-in plural types. High-level languages such as Java and C # do not provide plural types.

Plural type 2c = 7 + 8j "3print (type (c))

Line 3 outputs the result:

Note: the plural type is written in the same way as in mathematics. If the word "I" is not recognized by Python, it will prompt for a syntax error.

02 string

There are three ways to represent strings in Python-single quotes, double quotes, and triple quotes. Single quotation marks and double quotation marks have the same function, and different programmers can use single or double quotation marks according to their own habits. PHP programmers may be more accustomed to using single quotation marks for strings, while C and Java programmers are used to using double quotation marks for strings. The use of single and double quotes in the following code is equivalent.

The use of single and double quotation marks is equivalent to "2str =" hello world! "# defines the string variable str and assigns the value" 3print (str) "4str = 'hello worldquotation' 5print (str)"

[code description]

Line 3 outputs the result:

Hello world!

Line 5 outputs the result:

Hello world!

The use of three quotes is a special syntax of Python. You can enter characters such as single quotation marks, double quotation marks, or line breaks in the three quotation marks.

The use of "triple quotation marks" 2str =''he say "hello world!"'"3print (str)

[code description]

The third line of code is enclosed in double quotes, and double quotes are output. Output result:

He say "hello world!"

Another use of three quotation marks is to make document strings. Each object in Python has a property _ _ doc__, which describes what the object does.

"three quotes make doc document" 2class Hello: "3'''hello class'''" 4def printHello (): "5'''print hello world'''" 6print ("hello world!") "7print (Hello.__doc__)" 8print (Hello.printHello.__doc__)

[code description]

Line 2 defines a class called Hello.

Line 3 is the description of the Hello class, which will be stored in the _ _ doc__ property of the class.

Line 4 defines a method printHello ().

Line 5 describes printHello () and stores the string in the function's _ _ doc__ property.

Line 6 outputs the result:

Hello world!

Line 7 outputs the contents of the _ _ doc__ attribute of Hello. Output result:

Hello class

Line 8 outputs the contents of the _ _ doc__ attribute of printHello (). Output result:

Print hello world

If you want to output a string that contains special characters (single quotes, double quotes, and so on), you need to use escape characters. The escape character in Python is "\", which is the same as that in C and Java. The escape operation only needs to be preceded by a "\" before the special character. The following code illustrates the escape use of special characters.

Escape character 2str ='he say:\ 'hello world!\' escape 3print (str)

[code description]

The single quotation marks in line 2 are special characters that need to be preceded by an escape character before "'". The output of the third line of code:

He say:'hello worldview'

Use double or triple quotation marks to directly output strings containing special characters without the need for escape characters.

Direct output of the special character "2str =" he say:'hello worldview'"" 3print (str) "4str ='he say:'hello worldview'" 5print (str) "

[code description]

Double quotation marks are used in the second line of code to indicate the string variable str, so Python can recognize that the single quotation marks inside the double quotation marks are just as output characters.

The output of the third line of code:

He say:'hello worldview'

Line 4 uses triple quotes to indicate the string variable str. Notice that the last single quotation mark is followed by a space so that Python can recognize the three quotation marks. If four single quotation marks are concatenated without leaving this space, the Python interpreter will not correctly recognize the three quotation marks. The following error is prompted:

SyntaxError: EOL while scanning single-quoted string

The output of line 5:

He say:'hello worldview'

Note: the output string contains single quotation marks. Use double quotation marks to indicate the string. On the contrary, when the output string contains double quotation marks, you can use single quotation marks to represent the string.

At this point, I believe you have a deeper understanding of "how to understand Python numbers and strings". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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