Basic Python data types and variables

The data type

As the name suggests, a computer is a machine that can do mathematical calculations, so it stands to reason that computer programs can handle all kinds of numbers. However, computers can process far more than numerical values, but also can process text, graphics, audio, video, web pages and other data, different data, need to define different data types. In Python, there are several types of data that can be handled directly:

The first group of letters is: Mengy, the second group is: 7762, and she will arrange to learn them in order. , whether you are big bull or small white, is want to change or want to enter the industry can come to understand progress together to learn! There are development tools, lots of dry goods and technical information to share!

The integer

Python can handle integers of any size, including negative integers, as mathematically written, such as 1,100, -8080, 0, and so on.

Because computers use binary, it is sometimes convenient to use hexadecimal integers, which are represented by the 0x prefix and 0-9, a-f, such as 0xFF00, 0xA5b4C3d2, and so on.

Floating point Numbers

Floating point numbers, which are decimals, are called floating point numbers because in scientific notation, the decimal position of a floating point number is variable; for example, 1.23×109 is equal to 12.3×108. Floating point numbers can be written mathematically, such as 1.23, 3.14, -9.01, and so on. But for very large or very small floating-point numbers, you have to use scientific notation, substituting 10 for e, 1.23×109 for 1.23e9, or 12.3E8, 0.000012 for 1.2E-5, and so on.

Integers and floating-point numbers are stored differently inside a computer, and integer operations are always exact. Yes!) Floating-point operations can be rounded off.

string

A string is any text enclosed in “” or “”, such as

‘abc’

“xyz”

And so on. Note that ” or “” is only a representation in and of itself, not part of a string, therefore, a string

‘abc’

only

These three characters. if

‘

It is also a character, so it can be enclosed in “”, for example

“I’m OK”

The contained characters are

‘

, the blank space,

These six characters.

If the string contains both

‘

Contain,

“

How to do? Escape characters can be used

To identify, for example:

'I\'m \"OK\"! '

The contents of the string represented are:

I'm "OK"!

Escape character

Can escape many characters, such as

Means newline,

Represents TAB characters

It has to escape itself, so

The character represented is

Print the string on Python’s interactive command line:

>>> print 'I\'m ok.'I'm ok.

If a string has a lot of characters that need to be escaped, add a lot

For simplicity, Python also allows use of

r”

said

‘ ‘

Internal strings are not escaped by default, you can try yourself:

>>> print '\\\t\\'\ \>>> print r'\\\t\\'\\\t\\

If there are many line breaks inside the string, use

It’s hard to read on a single line, so Python allows it for simplicity

“‘… ‘ ‘ ‘

The format represents multiple lines of content, you can try it yourself:

>>> print '''line1... line2... line3'''line1

The above is the interactive command line input, if written as a program, is:

print '''line1

Multiline string

“‘… ‘ ‘ ‘

I could also add it out front

Use, please test yourself.

Boolean value

Boolean values and Boolean algebra are exactly the same representation, a Boolean value is only

True

False

Two values, either

True

, either

False

In Python, you can use it directly

True

False

Represents a Boolean value (case sensitive), which can also be computed by a Boolean operation:

>>> TrueTrue>>> FalseFalse>>> 3 > 2True>>> 3 > 5False

Boolean values can be used

and

not

Operation.

and

An operation is and an operation only if everything is

True

and

The result of the operation is

True

>>> True and TrueTrue>>> True and FalseFalse>>> False and FalseFalse

An operation is an or operation as long as one of them is

True

And the result of that is

True

>>> True or TrueTrue>>> True or FalseTrue>>> False or FalseFalse

not

The operation is not an operation, it is a unary operator, the

True

become

False

become

True

>>> not TrueFalse>>> not FalseTrue

Booleans are often used in conditional judgments, such as:

if age >= 18: print 'adult'else: print 'teenager'

A null value

A null value is a special value in Python

None

Said.

None

Not to be understood as

Because the

Is meaningful, and

None

Is a special null value.

In addition, Python provides lists, dictionaries, and other data types, as well as the ability to create custom data types, which we’ll cover later.

variable

The concept of variables is basically the same as equation variables in junior high school algebra, except that in computer programs, variables can be not only numbers, but also any data type.

A variable in a program is represented by a variable name, which must be uppercase, numeric, and

And cannot start with a number, such as:

a = 1

variable

It’s an integer.

t_007 = 'T007'

variable

t_007

It’s a string.

Answer = True

variable

Answer

Is a Boolean value

True

In Python, the equal sign

An assignment statement can assign any data type to a variable, the same variable can be repeatedly assigned, and can be different types of variables, for example:

A = 123 # a print a

Languages in which the variable itself is of variable type are called dynamic languages, as opposed to static languages. Static languages must specify the type of a variable when defining it, and an error will be reported if the assignment does not match the type. For example, if Java is a static language, the assignment statement looks like this (// represents a comment) :

int a = 123; // a is an integer type variable a = "ABC"; // Error: cannot assign strings to integer variables

This is why dynamic languages are more flexible than static languages.

Do not equate the equal sign of an assignment statement with the equal sign of mathematics. For example:

x = 10x = x + 2

If you think about it mathematically

x = x + 2

That’s not true anyway. In a program, assignment evaluates the expression on the right first, okay

x + 2

, get the result

, and assign to the variable

. Due to the

The previous value was zero

, after reassigning,

The value of the into

Finally, it is important to understand how variables are represented in computer memory. When we write:

a = 'ABC'

When, the Python interpreter does two things:

One is created in memory

‘ABC’

String;
Creates a file in memory named

a

Variable and point it to

‘ABC’

.

You can also put a variable

Assign to another variable

, this operation is actually a variable

Pointing to the variable

To point to data, such as the following code:

a = 'ABC'b = a

The last line prints out the variable

What is the content of

‘ABC’

‘XYZ’

? If you understand it mathematically, you get the wrong answer

and

Same thing, it should be

‘XYZ’

But in fact

The value is

‘ABC’

Let’s run the code line by line to see what happens:

perform

a = ‘ABC’

The interpreter creates the string

‘ABC’

And variables

And put the

Point to the

‘ABC’

perform

b = a

The interpreter creates the variable

And put the

Point to the

String to point to

‘ABC’

perform

a = ‘XYZ’

, the interpreter creates the string ‘XYZ’ and puts

Change the direction of

‘XYZ’

, but

Has not changed:

So, finally, print the variable

Of course

‘ABC’

constant

A constant is a variable that cannot be changed. For example, the mathematical constant π is a constant. In Python, constants are usually represented by all-caps variable names:

PI = 3.14159265359

But in fact

Is still a variable, and Python has no mechanism to guarantee it at all

Will not be changed, so using all uppercase variable names for constants is just a common usage if you must change the variable

No one can stop you.

To finally explain why integer division is accurate, try:

>>> 10 / 33

You read that right. Integer division is always an integer, even if you can’t divide it all. To do the exact division, simply replace one of the integers with a floating-point number and do the division:

>>> 10.0 / 33.3333333333333335

Since integer division only takes the integer part of the result, Python also provides a remainder operation that yields the remainder of dividing two integers:

> > > 10% 31

Whether you divide an integer or take a remainder, the result is always an integer, so the result of an integer operation is always accurate.

summary

Python supports a variety of data types. Inside the computer, any data can be considered an “object”, and variables are used to refer to these data objects in the program. Assigning values to variables associates data with variables.

Basic Python data types and variables

Related Posts

Problem resolved: ORA-04030 private memory exceeded

Review Java generics after a few years of work

Java programming ideas pick up (11) exceptions