魔力Python——我踩过的各种坑

Posted 2020-11-16 流云封心

1.函数与内置函数

 

def func(a=1, b=2, l=[]):
    l.append(a + b)
    print(l)

func(1,2)
func(3,4,[])
func(5,6)
#结果:
#[3]
#[7]
#[3, 11]

filter:

lst = filter(lambda n:n%3 == 1,range(10))
print(len(list(lst)))
print(len(list(lst)))
#结果:
#3
#0
# filter返回的是迭代对象, 这个迭代器只能迭代一次(list(lst)),迭代完成就完了. 第二次(list(lst)),执行返回的是空.
# 但如果你把结果做为list放到内存里, 就没有这个问题了,只是如果list很大的话,内存占用多,效率会下降,好的做是把这些操作串在一起, 一次完成.

 

 

2.迭代器,生成器与装饰器

 

def Generator():
    value = yield 1
    yield value
gen = Generator()
print(gen.send(1))
#结果:
#报错:TypeError: can\'t send non-None value to a just-started generator
#解决方法:第一个用next接收,接下来再用send

 

v = [lambda :x for x in range(10)]
print(v)
# print(v[0])
# print(v[0]())
v = (lambda  :x for x in range(10))
print(v)
for i in range(10):
    print(v.__next__()())
print(v[0])
#最后一个print报错,TypeError: \'generator\' object is not subscriptable.
#原因:第二个生成的v实际上是生成器(此处要注意生成器的两种生成手段,一个是如此生成,另一个是定义出来的用yield挂起值),用v.__next__导出的是函数,此时调用发现从0到9依次输出.而生成器怎么可能像列表那样操作呢?
#PS:生成器两种写法:
#1.只要把一个列表生成式的[]改成()，就创建了一个generator
#2.如果一个函数定义中包含yield关键字，那么这个函数就不再是一个普通函数，而是一个generator

装饰器的典型错误: 

flag = True


def wrapper(func):
    def inner(*args, **kwargs):
        if flag:
            ret = func(*args, **kwargs)
            return ret

    return inner


@wrapper
def wahaha():
    print(\'wahaha\')
    return True


flag = False
ret = wahaha()
print(ret)
#输出结果是None,你能想到么?因为里面关了,所以直接不走了,输出none.并不是像想象中的走主函数的语句块,不然装饰器意义何在呢?就是要在装饰器里面调用的呀!

 

3.正则表达式与re模块

 

demo1:
import re
ret = re.search(r\'<(w+)>(\\w+)<(\\\\\\w+)>\',r\'<title>qqxing<\\title>\')
print(ret.group())

demo2:
import re
ret = re.search(r\'<(\\w+)>(\\w+)<(\\\\w+)>\',r\'<title>qqxing<\\title>\')
print(ret.group())

#demo1和demo2错误相同.
#AttributeError: \'NoneType\' object has no attribute \'group\'
#解决方案:demo1应该是\\w+ ;  demo2应该是\\\\\\

demo3:
import re
ret = re.search(r\'<(?P<tab1>\\w+)>(?P<content>\\w+)<(\\\\\\w+)>\',r\'<title>qqxing<\\title>\')
print(ret.group(\'<content>\'))

#IndexError: no such group
#解决方案:去掉<>

demo4:

import re
ret = re.search(\'<(?P<tag>\\w+)>(\\w+)<\\\\(?P=<tag>)>\',r\'<h1>wahaha<\\h2><\\h1>\')
print(ret.group())

#sre_constants.error: unbalanced parenthesis at position 26
#解决方案:第一个前面加个r,即r\'<(?P<tag>\\w+)>.*?<\\\\(?P=tag)>\'

 

 

 4.面对对象

 

class Goods:
    def __init__(self,name,price,number):
        self.__name = name
        self.price = price
        self.number = number
    def pay(self):
        print(self.__name)
        print(self.price)
    def __add__thing(self):
        print(\'ok\')


apple = Goods(\'apple\',5,10)
print(apple.price)
print(apple.number)
# 报错!!!print(apple.__name)#apple.__name调用不出来#AttributeError: \'Goods\' object has no attribute \'__name\'
print(apple.__dict__)
print(apple._Goods__name)#_类名__属性名才能调用出来
apple.pay()
# 报错!!! apple.__add__thing#AttributeError: \'Goods\' object has no attribute \'__add__thing\'
print(apple._Goods__add__thing)#类方法调用情况<bound method Goods.__add__thing of <__main__.Goods object at 0x00000000023D7E80>>
apple._Goods__add__thing()#正常输出

 

 5.异常

 

#demo1:
with open(\'course_st_info\',\'rb\')as f:
     print(pickle.load(f))
#由于之前没有该文件,所以报错.
#报错内容:EOFError: Ran out of input
#修正结果
        try:
            with open(\'course_st_info\',\'rb\')as f:
                print(pickle.load(f))
        except EOFError:
            pass

#demo2:

while 1:
    try:
        with open(\'course_all_info\', \'ab\')as f:
            pickle.load(f)
    except EOFError:
        break

#报错内容:io.UnsupportedOperation: read
#原因:读取格式不对
#解决方案:将ab改为rb.

 

6. 网络编程

 

#server
import socket
sk = socket.socket()
sk.bind((\'127.0.0.1\',9001))
while 1:
    conn,addr = sk.accept()
    while 1:
        username = \'smith\'
        password = \'123\'
        usn = conn.recv(1024).decode(\'utf8\')
        psw = conn.recv(1024).decode(\'utf8\')
        if usn ==username and psw == password:
            msg = \'登录成功\'
        else:
            msg = \'登录失败\'
        conn.send(msg.encode(\'utf8\'))
    conn.close()
sk.close()
#报错:OSError: [WinError 10022] 提供了一个无效的参数。
#在sk.bind((\'127.0.0.1\',9001))下面写sk.listen()
#当缺少监听的时候接收本来就是不可能的事情


#client
import socket
sk = socket.socket()
sk.connect(\'127.0.0.1\',9001)
while 1:
    usn1 = input(\'请输入账号:\').strip()
    psw1 = input(\'请输入密码:\').strip()
    sk.send(usn1.encode(\'utf8\'))
    sk.send(psw1.encode(\'utf8\'))
    msg1 = sk.recv(1024).decode(\'utf8\')
    print(msg1)
    if \'成功\' in msg1:break
sk.close()
#报错:TypeError: connect() takes exactly one argument (2 given)
#这种错误一般是sk.connect处.
#sk.connect后面应该跟元组,所以是sk.connect((\'127.0.0.1\',9001))

 

import socket

sk = socket.socket(socket.SOCK_DGRAM)
server_addr = (\'127.0.0.1\', 9001)
while 1:
    content = input(\'>>>\')
    sk.sendto(content.encode(\'utf8\'), server_addr)
    msg, _ = sk.recvfrom(1024)
    print(msg.decode(\'utf8\'))
sk.close()

#OSError: [WinError 10057] 由于套接字没有连接并且(当使用一个 sendto 调用发送数据报套接字时)没有提供地址，发送或接收数据的请求没有被接受。
#原因:sk = socket.socket(type = socket.SOCK_DGRAM)

 

#server:
import json
import socket
import hashlib
import struct


def get_sha1(username,password):
    sha1 = hashlib.sha1(username.encode(\'utf8\'))
    sha1.update(password.encode(\'utf8\'))
    return sha1.hexdigest()

def get_userinfo(filename_userinfo):
    with open(filename_userinfo, encoding=\'utf8\') as f:
        for line in f.readlines():
            user,pwd = line.strip().split(\'|\')
            yield user,pwd

sk = socket.socket()
sk.bind((\'127.0.0.1\',9001))
sk.listen()

conn,addr = sk.accept()


flag = 1
while flag:
    num = conn.recv(4)
    num = struct.unpack(\'i\', num)[0]
    bytes_dic1 = conn.recv(num)
    str_dic1 = bytes_dic1.decode(\'utf8\')
    dic1 = json.loads(str_dic1)
    dic1[\'password\'] = get_sha1(dic1[\'username\'], dic1[\'password\'])
    for user,pwd in read:
        if dic1[\'username\'] == user and dic1[\'password\'] == pwd:
            bytes_msg = \'登录成功\'.encode(\'utf8\')
            struct_len = struct.pack(\'i\',len(bytes_msg))
            conn.send(struct_len)
            conn.send(bytes_msg)
            flag = 0
            break
    else:
        flag += 1
        if flag == 4:
            bytes_msg = \'登录失败,请明天再试\'.encode(\'utf8\')
            struct_len = struct.pack(\'i\', len(bytes_msg))
            conn.send(struct_len)
            conn.send(bytes_msg)
            conn.close()
        bytes_msg = \'登录失败,请明天再试\'.encode(\'utf8\')
        struct_len = struct.pack(\'i\', len(bytes_msg))
        conn.send(struct_len)
        conn.send(bytes_msg)

conn.close()
sk.close()

#client:
import json
import socket
import hashlib
import struct


def get_md5(username, password):
    md5 = hashlib.md5(username.encode(\'utf8\'))
    md5.update(password.encode(\'utf8\'))
    return md5.hexdigest()

for i in range(3):
    username = input(\'用户名:\').strip()
    password = input(\'密  码:\').strip()



    sk = socket.socket()
    sk.connect((\'127.0.0.1\', 9001))


    password = get_md5(username, password)
    dic1 = {\'username\': username, \'password\': password}
    str_dic1 = json.dumps(dic1)
    bytes_dic1 = str_dic1.encode(\'utf8\')
    bytes_len = struct.pack(\'i\', len(bytes_dic1))

    sk.send(bytes_len)
    sk.send(bytes_dic1)

    num = sk.recv(4)
    num = struct.unpack(\'i\',num)[0]
    bytes_msg = sk.recv(num)
    print(bytes_msg.decode(\'utf8\'))

sk.close()


#报错:num = struct.unpack(\'i\', num)[0]
#struct.error: unpack requires a buffer of 4 bytes
#原因:经查看是循环时候报错,由此推出是因为client端未循环输入username和password的问题.
#报错:非套接字OSError: [WinError 10038] 在一个非套接字上尝试了一个操作。
#原因:查看是否进行了conn.close()但还是在进行连接.

 

7.MySQL

ERROR 1054(42S22):Unknown column \'smith\' in \'field list\'

解决方案:把变量加上引号变为字符串即可.

 

8.Django

报错: \'Did you install mysqlclient or MySQL-python?\' % e
django.core.exceptions.ImproperlyConfigured: Error loading MySQLdb module: No module named \'MySQLdb\'.
Did you install mysqlclient or MySQL-python?

解决方案:忘配置与settings同级的__init__的文件了.写如下:

import pymysql
pymysql.install_as_MySQLdb()

 

9.通用

9.1 编码问题

 

table1 = pd.read_excel(r"C:\\Users\\Administrator\\Desktop\\数据1.xls")
table2 = pd.read_excel(r"C:\\Users\\Administrator\\Desktop\\trans.xls")

(unicode error) \'unicodeescape\' codec can\'t decode bytes in position 2-3: truncated \\UXXXXXXXX escape

解决方法:记得在路径处加r. 避免转义.