Python填坑之路(持续更新)

1、re的正则匹配字符串中不能带空格，否则无法匹配！

例如：

>>> re.findall('z','z ff')

此时要将空格去掉再匹配：

>>> a = 'z ff'.replace(' ','')
>>> re.findall('z',a)

 

2、验证匹配关系

如：

a = ['a','b','c','d','e']
b = ['a','e']

判断b是否属于a（b∈a），需要用set()将a和b均转化成集合再比较：

a = set(a)
b = set(b)
if b <= a:
    print('xxx')

 

3、str转int （读取文件中适用）

a = '100'
b = int(a)

报错：ValueError: invalid literal for int() with base 10

原因是str中包含非数字成分，所以要去除非数字成分，即可解决：

c = re.sub("\D", "", a)
b = int(a)

这里\D表示非数字成分

 

4、连续退出两层循环：

for a in xrange(10):
    for b in xrange(20):
        if something(a, b):
            # Break the inner loop...
            break
    else:continue        # Continue if the inner loop wasn't broken.
    break    # Inner loop was broken, break the outer.

 

5、socket.send()无法直接传入变量，如socket.send('hello,%s' % user)将会报错。此时要先定义好变量再传入：

data = 'hello,%s' % user
socket.send(data.encode('utf-8'))

 

6、string类型转成raw string类型(即r'')：

背景：

通过输入(input)或者socket传输得到的变量可能会是类似这样的"E:\\"，当使用或打印变量时就会变成'E:\'，也即少了一个'\'，只有将string类型转成raw string类型(即r'')才能保留多个'\'，若接收的变量a值为'E:\\'，我们可以采用 repr(a)[1:-1] 的方式保留'\'

 

7、当文件以二进制的格式打开时不能带编码方式，如：

with open(ab_file, "wb", encoding='utf-8') as f:

会报错：ValueError: binary mode doesn't take an encoding argument

去掉编码类型即可

 

8、pycharm中执行python程序时自动弹出Edit configuration配置项，无法执行程序。
原因：pycharm环境配置错误，例如python解释器找不到。
解决：Settings–>Project: python–>Python Interpreter设置正确的python解释器。

9、访问同一个类中另一个函数的变量：
在定义变量时加上 self. ，后期访问前加上对函数的调用，如：

class A():
    def b(self):
        self.b1 = 3
    def c(self):
        c1 = self.b1 + 5
        print(c1)
obj = A()
obj.b()
obj.c()

# 此时打印c1的结果是8。这里是将b1定义为成员变量，只要在类中都可以访问。
注意：调用时一定要先调用b方法，否则找不到b1变量的声明会报错。

 

10、中断函数，不往下执行后面的代码：

return xxx

 

11、已经声明的队列（queue）属性不可更改，即没有设置队列持久化的队列不可重新设置成队列持久化，反之亦然。否则会报以下错误：

pika.exceptions.ChannelClosed: (406, "PRECONDITION_FAILED - inequivalent arg 'durable' for queue 'hello1' in vhost '/': received 'false' but current is 'true'")

 

 12、Django admin搜索时报错：

django.core.exceptions.FieldError: Related Field got invalid lookup: icontains

　　原因：search_fields中的项存在非字符类型（特别注意没有__str__的外键字段，需要指向到表中的字符字段），修改如下：

search_fields = ['user__username', 'user__position', 'message']

　　再执行还是报错：

pymysql.err.InternalError: (1271, "Illegal mix of collations for operation 'like'")

　　原因：在 MySQL 5.5 以上，在编程时要对每个字段进行查找，在执行时可能就会出现时间字段 like '%中文%' 这种语法，需要修改源码：即将所有icontains的值与其上的contains一致

site-packages/django/db/backends/mysql/base.py
...
'icontains': 'LIKE BINARY %s',
...
'icontains': "LIKE BINARY CONCAT('%%', {}, '%%')",

 

13、Django执行migrate时报错：Duplicate column name

(helpdesk) [root@Fone helpdesk]# python manage.py migrate
Operations to perform:
  Apply all migrations: admin, auth, captcha, contenttypes, django_celery_beat, helpdesk, sessions, sites
Running migrations:
  Applying admin.0002_logentry_user...Traceback (most recent call last):
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/db/backends/utils.py", line 85, in _execute
    return self.cursor.execute(sql, params)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/db/backends/mysql/base.py", line 71, in execute
    return self.cursor.execute(query, args)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/pymysql/cursors.py", line 170, in execute
    result = self._query(query)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/pymysql/cursors.py", line 328, in _query
    conn.query(q)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/pymysql/connections.py", line 517, in query
    self._affected_rows = self._read_query_result(unbuffered=unbuffered)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/pymysql/connections.py", line 732, in _read_query_result
    result.read()
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/pymysql/connections.py", line 1075, in read
    first_packet = self.connection._read_packet()
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/pymysql/connections.py", line 684, in _read_packet
    packet.check_error()
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/pymysql/protocol.py", line 220, in check_error
    err.raise_mysql_exception(self._data)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/pymysql/err.py", line 109, in raise_mysql_exception
    raise errorclass(errno, errval)
pymysql.err.InternalError: (1060, "Duplicate column name 'user_id'")

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "manage.py", line 15, in <module>
    execute_from_command_line(sys.argv)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/core/management/__init__.py", line 381, in execute_from_command_line
    utility.execute()
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/core/management/__init__.py", line 375, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/core/management/base.py", line 316, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/core/management/base.py", line 353, in execute
    output = self.handle(*args, **options)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/core/management/base.py", line 83, in wrapped
    res = handle_func(*args, **kwargs)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/core/management/commands/migrate.py", line 203, in handle
    fake_initial=fake_initial,
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/db/migrations/executor.py", line 117, in migrate
    state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/db/migrations/executor.py", line 147, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/db/migrations/executor.py", line 244, in apply_migration
    state = migration.apply(state, schema_editor)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/db/migrations/migration.py", line 124, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/db/migrations/operations/fields.py", line 84, in database_forwards
    field,
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/db/backends/mysql/schema.py", line 42, in add_field
    super().add_field(model, field)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/db/backends/base/schema.py", line 435, in add_field
    self.execute(sql, params)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/db/backends/base/schema.py", line 133, in execute
    cursor.execute(sql, params)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/db/backends/utils.py", line 100, in execute
    return super().execute(sql, params)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/db/backends/utils.py", line 68, in execute
    return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/db/backends/utils.py", line 77, in _execute_with_wrappers
    return executor(sql, params, many, context)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/db/backends/utils.py", line 85, in _execute
    return self.cursor.execute(sql, params)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/db/utils.py", line 89, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/db/backends/utils.py", line 85, in _execute
    return self.cursor.execute(sql, params)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/db/backends/mysql/base.py", line 71, in execute
    return self.cursor.execute(query, args)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/pymysql/cursors.py", line 170, in execute
    result = self._query(query)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/pymysql/cursors.py", line 328, in _query
    conn.query(q)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/pymysql/connections.py", line 517, in query
    self._affected_rows = self._read_query_result(unbuffered=unbuffered)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/pymysql/connections.py", line 732, in _read_query_result
    result.read()
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/pymysql/connections.py", line 1075, in read
    first_packet = self.connection._read_packet()
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/pymysql/connections.py", line 684, in _read_packet
    packet.check_error()
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/pymysql/protocol.py", line 220, in check_error
    err.raise_mysql_exception(self._data)
  File "/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/pymysql/err.py", line 109, in raise_mysql_exception
    raise errorclass(errno, errval)
django.db.utils.InternalError: (1060, "Duplicate column name 'user_id'")

原因：/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/contrib/admin/migrations/0002_logentry_user.py与原有表结构冲突

解决方案：删除/root/.virtualenvs/helpdesk/lib/python3.7/site-packages/django/contrib/admin/migrations/中的所有迁移文件，重新执行makemigrations和migrate

注意：

Ⅰ. 项目原始使用django原生User表，当项目跑了一段时间要新增User字段（继承AbstractUser）时，要注意models中是否有关联到User表的字段（尽量使用settings.AUTH_USER_MODEL便于扩展），在迁移数据时注意不要将表结构覆盖了。

Ⅱ. 当迁移数据一直报错无法解决时使用以下方式迁移数据：

　　⒈ 将数据导出（-t 参数表示只导出数据，只用数据库名表示导出表结构和数据）

mysqldump -uroot -p -B {数据库名} --tables {表名} -t > backup_data.sql
mysqldump -uroot -p {数据库名} > backup_old.sql

　　⒉ 删除/创建数据库

drop database {数据库名};
create database {数据库名} charset='utf8';

　　⒊ 删除迁移文件（注意不要将migrations目录下的__init__.py误删）

rm {工程目录}/migrations/00*.py
rm {虚拟环境}/site-packages/django/contrib/admin/migrations/00*.py

　　4. 生成迁移文件&创建表结构

python manage.py makemigraions
python manage.py migrate

　　⒌ 导出数据（backup_new.sql）与原数据（backup_old.sql）进行比对

mysqldump -uroot -p {数据库名} > backup_new.sql
vimdiff backup_new.sql backup_old.sql

　　注意：此步是为了防止django创建表结构的字段顺序不同而出现的数据无法同步问题，如下：

　　（补图）

　　出现此类问题时需要将新表字段创建顺序改为旧表的创建顺序，保留有改变的表结构，再执行数据导入。

　　⒍ 去除backup_data.sql中已删除表数据，或将新增表的数据单独抽出来（抽出来的数据.sql还需要再执行一次导入）

　　⒎ 执行数据导入

mysql -uroot -p {数据库名} < backup_new.sql   # 如果步骤5中比对有改变的话需要执行
mysql -uroot -p {数据库名} < backup_data.sql
mysql -uroot -p {数据库名} < 抽出来的数据.sql   # 如果有的话

　　⒏ 启动项目检查数据展示情况

python manage.py runserver 0:8001

　　

14、外部调用项目models：

要在导入models之前加上：

import os, sys

#如果放在project目录，就不需要在配置绝对路径了
pro_dir = os.getcwd()

sys.path.append(pro_dir)
os.environ.update({"DJANGO_SETTINGS_MODULE": "p1.settings"})   # 后面是项目的settings

import django
django.setup()

from p1.models import .

注意代码顺序不能改