def pfff(x,n=2,*,name,clss):
    s=1
    while n>0:
        s=s*x
        n=n-1
    print(s,",the student is",name,"in class",clss)
    return

https://www.liaoxuefeng.com/wiki/1016959663602400/1017024645952992

2021/7/27 Start as soon as possible

Catalog

review ：

  About coding ：

Python Basics ：

List&Tuple：

List

tuple

conditional ：

If sentence ：

  Loop statement ：

 dict&set：

dict

Set:

Volatile variables 、 Keyword parameters and named keyword parameters **highly important

Volatile variables

Keyword variables ：

​ Name keyword parameters ：

function ：

Recursive function ：

Advanced features

section ：

iteration ：

List generation ：

generator ：

iterator ：

review ：

python Its advantage lies in its perfect basic code base , The disadvantage is （ comparison C） Slow operation （ But the fact does not affect ）

win+R→cmd Enter→python（ The sign is >>>)

exit() sign out

If you use VS code, You need to switch directories

Then input and output ：（ Double quotation marks and single quotation marks can be used to represent strings ）

Run with the command line ：

 python With “#” Start commenting , Express the format in indentation （ Therefore, you should check the indentation after copying and pasting ）, Case sensitive , Escape character "\"

name=input('your name is： ')
print(name,"Say yohoho~ \\n"r'\n\\n')
print("Somalian Pirates We!")
print("Somalian",'Pirates',"We!")

  About coding ：

ASCII code （ Case letters + Numbers ）→ Countries add their own language characters （ China ：GB2312)→ Internationally Unicode（ Usually two bytes ）→ To simplify generation UTF-8（ Different number of bytes , One English letter , Chinese characters are generally three, some four ）

In computer memory , Unified use Unicode code , When you need to save to a hard disk or need to transfer , Just switch to UTF-8 code .

When editing with Notepad , Read from file UTF-8 The characters are converted to Unicode Characters in memory , After editing , Save it with Unicode Convert to UTF-8 Save to file .

When browsing the web , The server will dynamically generate Unicode Content to UTF-8 Then transfer to browser , So you can see a lot of source codes of web pages that are similar to <meta charset="UTF-8" /> Information about , It means that the web page is using UTF-8 code .

print(ord(' Ha '))
print(chr(123456))

Python Basics ：

List&Tuple：

List

Is the most commonly used variable form , Elements can be strings 、 Numbers 、 Boolean value, etc

chrters=['Pirates',"We"]
print(chrters)
print(len(chrters))
print(chrters[0])
print(chrters[-1])
chrters.append("!")
print(chrters)
chrters.insert(0,"Somalian")
print(chrters)
chrters.pop(3)
print(chrters)
chrters[2]="You"
print(chrters)

  The running result is ：

tuple

comparison list,tuple You cannot add, delete, or modify , in other words applend、pop、insert None of these functions can be used , Force the display ：

  Its advantage is that it can guarantee tuple Will not be tampered with later . You can still output and get the length according to the position . It is worth noting that , If it is a number as an element , Parentheses may be considered mathematical operators , So we can distinguish by adding a comma .（a=() It's an empty tuple）

chrters=('Pirates',"We",1)
print(chrters)
print(len(chrters))
print(chrters[-1])
chch=(1,)
print(chch)

Besides , If you put one list As tuple An element of , We can still modify list Internal elements （tuple Only the corresponding list It is the same. ）

L = [
    ['Apple', 'Google', 'Microsoft'],
    ['Java', 'Python', 'Ruby', 'PHP'],
    ['Adam', 'Bart', 'Lisa']
]
#  Print Apple:
print(L[0][0])
#  Print Ruby:
print(L[1][2])
#  hold Java become C++：
L[1].insert(0,"C++")
print(L[1])

conditional ：

If sentence ：

Note that the indentation , Add a colon at each step ."elif"

a=int(input("your age is:"))
if a<=0 or a>=125:
    print("It is nonsense!")
elif a<=12:
    print("you are a child")
elif a<=18:
    print("you are a teenager")
else:
    print("you are an adult")

  Loop statement ：

a=("Somalian",'Pirates',"We","!")
for aa in a:
    if aa!='!':
        print("Say",aa,"!")
i=1
while i<=4:
    print("say i=",i)
    i=i+1

Output is ：

 dict&set：

dict

The difference in list Establish one-to-one correspondence between ordinal numbers and elements ,dict（ Full name dictionary） Is to use the key - value （key-value） Corresponding to the . comparison list,dict It takes more memory but calls faster , yes “ Trade space for time ” Purpose .key It is used for calling , Therefore, it cannot be variable , Can be a string （string）、 Numbers 、tuple But it can't be list.

dict={"Alice":'good','Bob':"Mif","Cindy":96}
print(dict["Alice"])
dict['David']='Howdy'
print(dict)
print(dict.get("Elsa"),"NOTHERE")
dict.pop("Bob")
print(dict)

  Output is ：

  try key：

# key=[1,2]
# dict[key]=1
key=(1,2)
dict[key]=1
print(dict)

Cancelled （ Try to use list As key） Show ：

The normal code shows ：

Set:

  function ：

https://docs.python.org/3/library/functions.html#abs

Did a random number guessing game hey hey

  It's still a very interesting clam

  Make it better ……

def my_guessfor5():
    n=input("in which edge: ")
    if n.isdigit()==0:
        print("Please enter an integer as edge!")
        return
    n=int(n)
    k=random.randint(0,n)
    t=input("How many times?: ")
    if t.isdigit()==0:
        print("Please enter an integer as times!")
        return
    t=int(t)
    tt=0
    pal=0
    while tt<t:
        pp=input("now guess!: ")
        if pp.isdigit()==0:
            print("Please enter an integer to guess!")
            continue
        pp=int(pp)
        if pp<k:
            print("It is too small.")
            tt=tt+1
        if pp>k:
            print("It is too large.")
            tt=tt+1
        if pp==k:
            print("Congratulations! You win after",tt+1,"times!")
            return
    if tt==t:
        print("I am sorry, you lost.")
    return

  The output is ~

  Let's do a little math

import math
def solvvve(a,b,c):
    if not (isinstance(a,(int,float))*isinstance(b,(int,float))*isinstance(c,(int,float))):
        print("Please enter numbers!")
        return
    a=float(a)
    b=float(b)
    c=float(c)
    dd=math.sqrt(b*b-4*a*c)
    x1=(-b+dd)/(2*a)
    x2=(-b-dd)/(2*a)
    return x1,x2

Change to a little math

def poww(x,n=2,b=0):
    s=1
    while n>0:
        s=s*x
        n=n-1
    s=s+b
    return s

Output it for fun

Be careful , In this case n=2 and b=0 All are default parameters （ If you don't need it, you can leave it unchanged ）. The default parameter must be set to the invariant object （ Otherwise, for example list Things that are , If it is used at a certain time , After that, you may always remember the changed appearance ）.

Volatile variables 、 Keyword parameters and named keyword parameters **highly important

Volatile variables

Normally , All the variables we input are certain （ For example, numbers are numbers , A string is a string ）【 Required parameters and default parameters 】.

However , For the following procedure , If we only use number（ instead of *number）,

def calu(*number,**pw):
    s=0
    for num in number:
        s=s+num
    print("answer is",s,"the stu:",pw)

We need to use cal([1,2]) perhaps cal((1,2)) Input tuple、list Call function in the form of .（ Otherwise it will show TypeError: calu() takes 1 positional argument but 2 were given） therefore , We want to use *number Instead of number, In this way, the program will turn the input lump into a tuple Lose it .（ It can be used cal(*(1,2)) Keep using tuple perhaps list For input ）

Keyword variables ：

**pw, Enter a dict, You don't have to type in , The call form is as ：

Name keyword parameters ：

def pfff(x,n=2,*,name,clss):
    s=1
    while n>0:
        s=s*x
        n=n-1
    print(s,",the student is",name,"in class",clss)
    return

  Output check Several times ：

  If you set the required parameters 、 Default parameters 、 Variable parameters 、 Name keyword parameters 、 Keyword parameters are written （ This order must be followed ）, It can be ：

def pfff(x,n=2,*numm,name,clss,**what):
    s=1
    while n>0:
        s=s*x
        n=n-1
    for num in numm:
        s=s+num
    print(s,",the student is",name,"in class",clss,"others:",what)
    return

Output it and try ：

  Teacher Liao's warm tips ：

function ：

Recursive function ：

def mutli(n,m):
    if m==1:
        return n
    else:
        return n+multi(n,m-1)

def move(n,a,b,c):
    if n == 1:
        print(a, '-->', c)
    if n>1:
        move(n-1,a,c,b)
        print(a, '-->', c)
        move(n-1,b,a,c)

Advanced features

section ：

L=list(range(100))
LL=L[::10]
LLL=L[:10:2]
LLLL=L[-10::5]
print("L=",L,"LL=",LL,"LLL=",LLL,"LLLL=",LLLL)

iteration ：

L=("Who","lives","in","a","pinapple","under","the","sea")
for i in L:
    print(i)

List generation ：

import sympy
l=[y for y in range(100) if sympy.isprime(y)]
print(l)

import os
l=[d for d in os.listdir(".")]
print(l)

This for The function of looping to generate lists in just one line of code is really amazing . Try a classic example ：

import numpy as np
L=np.random.randn(15)
l=[d for d in L if d>0]
ll=[d if d>0 else 0 for d in L]
print("L=",L,"\n l=",l,"\n ll=",ll)

  among L It is a randomly generated one with 15 A list of elements , Its distribution conforms to 0 Is the central normal distribution .l Extract all of them greater than 0 The item ,ll It's a L Items smaller than zero are classified as 0.

generator ：

# Generate the Fibonacci sequence - Circular Edition 
nn=int(input("input:")) # Need to use int() Convert to number 
def fibb(N):
    i,a,b=1,1,1
    while i<N:
        a,b=b,a+b
        i=i+1
        yield a # Need to be in the loop yielda
    return 'success！yohoho~'#'' Represents the output string 
n=fibb(nn)
while True:
    try:
        t=next(n)
        print("new:",t)
    except StopIteration as e: #StopIteration Catch errors for output 
        print("output:",e.value)
        break # It must be added, or it will be output all the time output

Output ：

  Yang hui triangle ：

# Yang hui triangle ： Output the parameters of each line 
nn=int(input("input:"))
def yhsj(N):
    yield [1]
    n=2
    a=[1,1]
    while n<=N:
        b=[1]
        t=0
        while t<n-2:
            t=t+1# Together with n-2 Time 
            b.append(a[t-1]+a[t])
        b.append(1)
        a=b
        n=n+1
        yield a
    return "END"
n=yhsj(nn)
while True:
    try:
        print("new:",next(n))
    except StopIteration as e:
        print("Output:",e.value)
        break

Teacher Liao's class homework ：

    yield [1]
    L=[1,1]
    while True:
        yield L
        L=[L[i]+L[i+1] for i in range(len(L)-1)]#len([1,1])=2 range(2):0,1
        L.append(1)
        L.insert(0,1)

iterator ：

First consider iterable、iteration：

Generators are Iterator object , but list、dict、str Although it is Iterable, But not Iterator.

hold list、dict、str etc. Iterable become Iterator have access to iter() function ：

from collections.abc import Iterable, Iterator
#L=123 #False F TypeError: 'int' object is not iterable
#L=[123] #True F T
#L=(123,) #True F T\
L=(x*x for x in range(12)) #T T T
L=iter(L)
#print(isinstance(L,Iterable))
print(isinstance(L,Iterator))