Django项目启动 AttributeError: ‘str‘ object has no attribute ‘decode‘ 问题

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System check identified no issues (0 silenced).
Exception in thread django-main-thread:
Traceback (most recent call last):
  File "D:\Anaconda3\lib\threading.py", line 980, in _bootstrap_inner
    self.run()
  File "D:\Anaconda3\lib\threading.py", line 917, in run
    self._target(*self._args, **self._kwargs)
  File "D:\Anaconda3\lib\site-packages\django\utils\autoreload.py", line 54, in wrapper
    fn(*args, **kwargs)
  File "D:\Anaconda3\lib\site-packages\django\core\management\commands\runserver.py", line 120, in inner_run
    self.check_migrations()
  File "D:\Anaconda3\lib\site-packages\django\core\management\base.py", line 453, in check_migrations
    executor = MigrationExecutor(connections[DEFAULT_DB_ALIAS])
  File "D:\Anaconda3\lib\site-packages\django\db\migrations\executor.py", line 18, in __init__
    self.loader = MigrationLoader(self.connection)
  File "D:\Anaconda3\lib\site-packages\django\db\migrations\loader.py", line 49, in __init__
    self.build_graph()
  File "D:\Anaconda3\lib\site-packages\django\db\migrations\loader.py", line 212, in build_graph
    self.applied_migrations = recorder.applied_migrations()
  File "D:\Anaconda3\lib\site-packages\django\db\migrations\recorder.py", line 73, in applied_migrations
    if self.has_table():
  File "D:\Anaconda3\lib\site-packages\django\db\migrations\recorder.py", line 56, in has_table
    return self.Migration._meta.db_table in self.connection.introspection.table_names(self.connection.cursor())
  File "D:\Anaconda3\lib\site-packages\django\db\backends\base\base.py", line 256, in cursor
    return self._cursor()
  File "D:\Anaconda3\lib\site-packages\django\db\backends\base\base.py", line 233, in _cursor
    self.ensure_connection()
  File "D:\Anaconda3\lib\site-packages\django\db\backends\base\base.py", line 217, in ensure_connection
    self.connect()
  File "D:\Anaconda3\lib\site-packages\django\db\backends\base\base.py", line 197, in connect
    self.init_connection_state()
  File "D:\Anaconda3\lib\site-packages\django\db\backends\mysql\base.py", line 231, in init_connection_state
    if self.features.is_sql_auto_is_null_enabled:
  File "D:\Anaconda3\lib\site-packages\django\utils\functional.py", line 80, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File "D:\Anaconda3\lib\site-packages\django\db\backends\mysql\features.py", line 82, in is_sql_auto_is_null_enabled
    cursor.execute('SELECT @@SQL_AUTO_IS_NULL')
  File "D:\Anaconda3\lib\site-packages\django\db\backends\utils.py", line 103, in execute
    sql = self.db.ops.last_executed_query(self.cursor, sql, params)
  File "D:\Anaconda3\lib\site-packages\django\db\backends\mysql\operations.py", line 146, in last_executed_query
    query = query.decode(errors='replace')
AttributeError: 'str' object has no attribute 'decode'
D:\Anaconda3\Lib\site-packages\django\db\backends\mysql\operations.py changed, reloading.
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System check identified no issues (0 silenced).
Exception in thread django-main-thread:
Traceback (most recent call last):
  File "D:\Anaconda3\lib\site-packages\django\db\backends\utils.py", line 82, in _execute
    return self.cursor.execute(sql)
  File "D:\Anaconda3\lib\site-packages\django\db\backends\mysql\base.py", line 71, in execute
    return self.cursor.execute(query, args)
  File "D:\Anaconda3\lib\site-packages\pymysql\cursors.py", line 148, in execute
    result = self._query(query)
  File "D:\Anaconda3\lib\site-packages\pymysql\cursors.py", line 310, in _query
    conn.query(q)
  File "D:\Anaconda3\lib\site-packages\pymysql\connections.py", line 548, in query
    self._affected_rows = self._read_query_result(unbuffered=unbuffered)
  File "D:\Anaconda3\lib\site-packages\pymysql\connections.py", line 775, in _read_query_result
    result.read()
  File "D:\Anaconda3\lib\site-packages\pymysql\connections.py", line 1156, in read
    first_packet = self.connection._read_packet()
  File "D:\Anaconda3\lib\site-packages\pymysql\connections.py", line 725, in _read_packet
    packet.raise_for_error()
  File "D:\Anaconda3\lib\site-packages\pymysql\protocol.py", line 221, in raise_for_error
    err.raise_mysql_exception(self._data)
  File "D:\Anaconda3\lib\site-packages\pymysql\err.py", line 143, in raise_mysql_exception
    raise errorclass(errno, errval)
pymysql.err.OperationalError: (1046, 'No database selected')

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

Traceback (most recent call last):
  File "D:\Anaconda3\lib\threading.py", line 980, in _bootstrap_inner
    self.run()
  File "D:\Anaconda3\lib\threading.py", line 917, in run
    self._target(*self._args, **self._kwargs)
  File "D:\Anaconda3\lib\site-packages\django\utils\autoreload.py", line 54, in wrapper
    fn(*args, **kwargs)
  File "D:\Anaconda3\lib\site-packages\django\core\management\commands\runserver.py", line 120, in inner_run
    self.check_migrations()
  File "D:\Anaconda3\lib\site-packages\django\core\management\base.py", line 453, in check_migrations
    executor = MigrationExecutor(connections[DEFAULT_DB_ALIAS])
  File "D:\Anaconda3\lib\site-packages\django\db\migrations\executor.py", line 18, in __init__
    self.loader = MigrationLoader(self.connection)
  File "D:\Anaconda3\lib\site-packages\django\db\migrations\loader.py", line 49, in __init__
    self.build_graph()
  File "D:\Anaconda3\lib\site-packages\django\db\migrations\loader.py", line 212, in build_graph
    self.applied_migrations = recorder.applied_migrations()
  File "D:\Anaconda3\lib\site-packages\django\db\migrations\recorder.py", line 73, in applied_migrations
    if self.has_table():
  File "D:\Anaconda3\lib\site-packages\django\db\migrations\recorder.py", line 56, in has_table
    return self.Migration._meta.db_table in self.connection.introspection.table_names(self.connection.cursor())
  File "D:\Anaconda3\lib\site-packages\django\db\backends\base\introspection.py", line 48, in table_names
    return get_names(cursor)
  File "D:\Anaconda3\lib\site-packages\django\db\backends\base\introspection.py", line 43, in get_names
    return sorted(ti.name for ti in self.get_table_list(cursor)
  File "D:\Anaconda3\lib\site-packages\django\db\backends\mysql\introspection.py", line 55, in get_table_list
    cursor.execute("SHOW FULL TABLES")
  File "D:\Anaconda3\lib\site-packages\django\db\backends\utils.py", line 99, in execute
    return super().execute(sql, params)
  File "D:\Anaconda3\lib\site-packages\django\db\backends\utils.py", line 67, in execute
    return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
  File "D:\Anaconda3\lib\site-packages\django\db\backends\utils.py", line 76, in _execute_with_wrappers
    return executor(sql, params, many, context)
  File "D:\Anaconda3\lib\site-packages\django\db\backends\utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
  File "D:\Anaconda3\lib\site-packages\django\db\utils.py", line 89, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "D:\Anaconda3\lib\site-packages\django\db\backends\utils.py", line 82, in _execute
    return self.cursor.execute(sql)
  File "D:\Anaconda3\lib\site-packages\django\db\backends\mysql\base.py", line 71, in execute
    return self.cursor.execute(query, args)
  File "D:\Anaconda3\lib\site-packages\pymysql\cursors.py", line 148, in execute
    result = self._query(query)
  File "D:\Anaconda3\lib\site-packages\pymysql\cursors.py", line 310, in _query
    conn.query(q)
  File "D:\Anaconda3\lib\site-packages\pymysql\connections.py", line 548, in query
    self._affected_rows = self._read_query_result(unbuffered=unbuffered)
  File "D:\Anaconda3\lib\site-packages\pymysql\connections.py", line 775, in _read_query_result
    result.read()
  File "D:\Anaconda3\lib\site-packages\pymysql\connections.py", line 1156, in read
    first_packet = self.connection._read_packet()
  File "D:\Anaconda3\lib\site-packages\pymysql\connections.py", line 725, in _read_packet
    packet.raise_for_error()
  File "D:\Anaconda3\lib\site-packages\pymysql\protocol.py", line 221, in raise_for_error
    err.raise_mysql_exception(self._data)
  File "D:\Anaconda3\lib\site-packages\pymysql\err.py", line 143, in raise_mysql_exception
    raise errorclass(errno, errval)
django.db.utils.OperationalError: (1046, 'No database selected')

Django启动时报错

问题原因：

• 从 Error信息中可以得知，这是 str编码的问题，而且还是和 mysql进行交互之间的编码问题。

• python3里面，字符串要先encode手动指定其为某一编码的字节码之后，才能decode解码。

SO:

　　点击最后一条异常信息的地址，将query = query.decode(errors='replace') 修改成 query = query.encode(errors='replace')