I’m going to learn Python secretly and surprise everyone (Day 1)

No offense to the title, but I thought the AD was fun and the mind map above is yours to take, because I can’t learn that much anyway

Okay, cut to the chase

The article directories

• • preface
  • Overview of the Python language
  • • Origins of the Python language
  • The data type
  • • Number data type
    • Container data type
    • STR string
    • • Yuan string
      • String formatting
    • List phenotype ([])
    • • List modification
    • Tuple type (())
    • Set set type ({})
    • Dict dictionary ({“aaa”:” BBB “,})
    • supplement
  • arithmetic
  • String splicing
  • Cast casting
  • • str()
    • int()
    • float()
    • To summarize
  • Standard input output
  • • The print () function
    • The input () function
    • • Pay attention to the point
  • Control statements
  • • Conditional control statement
    • • If judgment
      • If… else…
      • The if… elif… the else
      • If the nested
    • For…… in circulation
    • • The range () function
      • Loop through the else statement
    • The while loop
    • other
    • • break
      • continue
      • pass
    • Compare the two cycles
  • Practice small projects
  • Long tail flow optimization

preface

This series of articles assumes that you have some basic knowledge of C or C++, because I started Python after learning a little C++. Thank you qi Feng for your support. This series of articles default you will baidu, will use the online compiler, because I am a surprise learning Python, the previous compilation environment has been deleted, but, I found that online compilation is really fun, waste that time to build that environment to do what, learn Python, will be poor that point to invite people to build environment money?

I don’t want much, just click on it. And then, the catalogue for this series, to be honest, MY preference is for the two Primer Plus books, so I’ll stick with their catalogue structure.

This series will also focus on cultivating your ability to do things on your own. After all, I cannot tell you all the knowledge points, so the ability to solve your needs by yourself is particularly important. Therefore, please do not regard the holes I have buried in the article as holes.

Image source: Black image of this article from “Wind Change Programming”

Overview of the Python language

Origins of the Python language

It’s a cliche, but sometimes there’s an unexpected benefit to going back to your roots, and it’s all in your personal savvy.

The author of Python, Guido von Rossum, was indeed Dutch. In 1982, Guido received a master’s degree in mathematics and computer science from the University of Amsterdam. But although he was a mathematician, he enjoyed computers more. In his words, despite his qualifications in mathematics and computer science, he always tended to do computer work and was keen to do anything related to programming.

At that time, he was exposed to and used languages such as Pascal, C, and Fortran. The basic design principle of these languages is to make machines run faster. The core of all compilers is to optimize the program so that it runs. To increase efficiency, languages also force programmers to think like computers in order to write programs that are more machine-friendly. It was a time when programmers wanted to wring every inch of computer power from their hands.

This way of thinking, however, troubles Guido. Guido knows how to write a feature in C, but the whole process takes a lot of time. His other option is the shell. However, the essence of the shell is to invoke commands. It’s not really a language. For example, shells have no numeric data types, and addition operations are complicated. In short, the shell does not fully mobilize the functions of the computer.

Guido hopes to have a language, this language can be like C language, can fully call the functional interface of the computer, but also like shell, can be easily programmed. Guido began writing a compiler/interpreter for Python in 1989 to pass the Christmas holidays. Python comes from Guido’s beloved Monty Python’s Flying Circus. He hopes the new language, called Python, will fulfill his vision of a fully functional, easy-to-learn, extensible language between C and shell. As a language design enthusiast, Guido has made (unsuccessful) attempts at designing languages. This time, too, it was pure hacking.

In 1991, the first Python compiler (and interpreter) was created. It is implemented in C and can call the C library (.so files). Since its birth, Python has had classes, functions, exceptions, core data types including lists and dictionaries, and an extended system based on modules.

The data type

Number data type

Int integer (positive integer 0 negative integer)

A float is a decimal number

Bool Boolean (True True False False)

Insert a complex type (which I haven’t used in over two years of writing code)

# 1.complexvar =5 + 6jcomplexvar =3 - 2j
　　　　　　print(type(complexvar))print(id(complexvar))

# 2.
		  complex(real, imaginary) res =complex(14.2)print(res) = > (14.2)
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Container data type

STR string

"" is a string caused by quotation marks, three kinds of quotation marks: single quotation marks double quotation marks triple quotation marks" "Escape character: \(1) to turn meaningful characters into meaningless characters (2) to turn meaningless characters into meaningful \n or \r\n: represents"Line"Meaning \ T: Stands for"One indent"Meaning \r: indicates that all characters after \r are placed at the beginning of the lineCopy the code

Other escape characters are not covered here

Features: Can be obtained, but can not be modified, order to obtain the data in the string: listlisttuplestupleIs exactly the same (forward subscript, reverse subscript)Copy the code

Yuan string

String formatting

“%d %f %s” syntax: “String” % (actual value)

The %d placeholder d represents integer data, and %nd represents n positions



Result: XXX bought 3 inflatable dolls

%f placeholder f indicates that floating point data is reserved with 6 decimal points by default. If f is preceded by a value, the corresponding decimal point is reserved according to the value



Result: Today Chinese cabbage 2.35 yuan a catty

Result: today Chinese cabbage 2.3 yuan a catty

The %s placeholder represents a string

List phenotype ([])

List modification

Tuple type (())

Set set type ({})

The setvar = {} data type displays a dict dictionary

Features: Cannot be obtained, nor can be modified, unordered, automatically remove duplicate data

Dict dictionary ({” aaa “:” BBB “,})

Features: The underlying hash algorithm is used to store the data as hashes, and the stored data is retrieved from the dictionary by key-value pairs. You can change it, just by replacing the key with the value that you want to change. In general, when you name dictionary keys, it's recommended to use strings, strings that are named by variables.Copy the code

supplement

Function to get data type: type() Function to get variable address: id()

arithmetic

String splicing

One great thing about Python that I really like is its string concatenation. Someone once said that programming is all about manipulating strings, and I think he’s right. Despite all the bells and whistles, it’s all about manipulating strings.

Anyway, I’ve had enough of the string manipulation in C/C++.

String concatenation in Python is simple. It uses the string concatenation symbol [+] to concatenate the variables to be concatenated.

But, since it’s string concatenation, the limitation is pretty obvious, you have to concatenate strings.

What if the pieces I have to put together are uneven? How to do? Don’t worry

Cast casting

str()

The STR () function converts data to its string type, whether int or float, by placing it in parentheses. This data can be transformed into a string. Isn’t that easy? We can convert integer type [153] into string type [153] by just one step of STR (number), successfully completing data concatenation.

int()

First of all, integer strings like'6'and'1'That can beint() function cast. Secondly, writing forms, such as Chinese, Martian or punctuation, cannot beint() function cast. Finally, decimal strings cannot be used because of Python syntax rulesint() function cast.Copy the code

float()

First of all,floatThe () function also places the data to be converted in parentheses, like this:float(Data). Second,floatThe () function can also convert integers and strings to floating point types. But at the same time, if the data inside the parentheses is a string, it must be a number.Copy the code

So, after the previous STR () and int() exercises, is the float() function a little clearer?

To summarize

Standard input output

Okay, so some of you might be wondering, why don’t you say I/O? Don’t worry!

The print () function

In parentheses are the numbersprint(520) in parentheses are single quotes.print('Let's play.') in parentheses are double quotation marks.print("Let's play.") when both single and double quotation marks exist in parentheses.print("Let's play"(Of course, the parentheses can also be triple quotation marks, refer to the above situation.Copy the code

The input () function

First, let’s take a look at how the input() function is used:

input('Please enter the name of the house you wish to attend in the following four boxes: gryffindor, Slytherin, Ravenclaw, Hufflepuff.')
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The input() function is the input function. In the example above, it would require you to enter the name of the house you would like to go to: in the following four boxes: gryffindor; Slytherin; Ravenclaw; Hufflepuff. So, when you write a question inside the function’s parentheses, the input() function displays the question as it is on the screen and waits for your answer to the question in the terminal area.

But why do we type the answer at the terminal? How about not typing? In fact, we can think of the input() function as a door between the real world and the code world. When a question is passed to us from the code world and we don’t answer it, the input() gate stays open, waiting for you to send an answer.

Pay attention to the point

Control statements

Conditional control statement

If judgment

One detail you might notice here is that there are several empty Spaces after the colon: and before the next line in the conditional code, but why? First of all, in computer language, the technical term for space is indentation. For example, when we write an essay, we should leave two Spaces blank. This is called the first line indentation. icon

With Python, colons and indentation are syntax. It helps Python distinguish between layers of code and understand the logic and sequence of conditional execution. [Note: indent is four Spaces] Here do not use TAB, on the matter of four Spaces, young people so lazy why, after forming a habit of many places are restricted.

If… else…

The if… elif… the else

For three or more conditions, we use Python’s multidirectional judgment command: if… Elif… The else… .

When more than three conditions are judged, elIF can be used for all intermediate conditions.

Elif is not followed by else

If the nested

For…… in circulation

The Python for loop can iterate over any sequence of items, such as a list or a string.

The syntax for the for loop is as follows:

for iterating_var in sequence:
   statements(s)
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for letter in 'Python':     # First instance
   print ('Current letter :', letter)
 
fruits = ['banana'.'apple'.'mango']
for fruit in fruits:        # second example
   print ('Current fruit :', fruit)
 
print ("Good bye!")
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As you can see, there is no pre-assignment for iterating_var in the template.

The range () function

for i in range(13.17) :print(i)
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for i in range(0.10.3) :print(i)
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Loop through the else statement

In Python, for… The for statement is the same as the normal statement. The else statement is executed when the loop completes normally, while… Same thing with else.

for num in range(10.20) :Iterate over numbers between 10 and 20
   for i in range(2,num): # Iterating by factor
      if num%i == 0:      # determine the first factor
         j=num/i          # Compute the second factor
         print ('%d = %d * %d' % (num,i,j))
         break            # exit the current loop
   else:                  # else part of the loop
      print (num, It's a prime number.)
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The while loop

a = 0                Define the variable a and assign it to it
while a < 5:         # Set a release condition: A must be less than 5
    a = a + 1  When the condition is met, do the job: add a+1
    print(a)   # Get on with business: Print out the result of a+1
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other

break

The # break statement is accompanied by a for loop
for.in. :...if. :break

The # break statement is accompanied by a while loop
while. (Condition):...if. :break
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continue

Continue means’ to go on ‘. This clause is also used inside the loop. When a condition is satisfied, the continue statement is fired, which skips the rest of the code and goes straight back to the beginning of the loop.

The # continue statement is accompanied by a for loop
for.in. :...if. :continue.The # continue statement is accompanied by a while loop
while. (Condition):...if. :continue.Copy the code

pass

Compare the two cycles

The biggest difference between a for loop and a while loop is whether the workload of the loop is determined. A for loop is like an empty room, and you don’t leave until you’ve done all the work. But a while loop is like a checkpoint pass, working until the checkpoint is not met

Practice small projects

Long tail flow optimization

The suggestion collects, otherwise paddling paddling can not find to.

I created a Python learning q & A group, interested friends can know: what is this group

The portal of the straight group:portal