字符串连接

Posted 2023-04-01

参考技术A 字符串连接 ( + 号连接)

可以使用 + 号连接任意两个字符串，连接字符串时，无论是使用单引号还是双引号创建的都可以。

Python 控制台运行：

>>> "Spam" + 'eggs'

'Spameggs'

>>> print("First string" + ", " + "second string")

First string, second string

字符串连接

即使你的字符串包含数字，它们仍然被添加为字符串而不是整数。将一个字符串加上数字中会产生一个错误，即使它们看起来相似，但它们是两个不同的实体。

print("2" + "2")

print(1 + '2' + 3 + '4')

尝试一下

结果：

22

Traceback (most recent call last):

  File "..\Playground\", line 3, in <module>

    print(1 + '2' + 3 + '4')

TypeError: unsupported operand type(s) for +: 'int' and 'str'

在将来的课程中，只会显示最后一行错误消息，因为它是唯一一个提供发生的错误类型的详细信息。

字符串操作（乘以整数）

字符串也可以乘以整数。这会产生原始字符串的重复版本。字符串和整数的顺序无关紧要，但字符串通常是放在前面的。

字符串不能与其他字符串相乘。即使浮点数是整数，字符串也不能乘以浮点数。

例如：

print("spam" * 3)

print(4 * '2')

print('17' * '87')

print('pythonisfun' * 7.0)

尝试一下

运行结果：

spamspamspam

2222

Traceback (most recent call last):

  File "..\Playground\", line 5, in <module>

    print('17' * '87')

TypeError: can't multiply sequence by non-int of type 'str'

MySql连接字符串

参考技术A The port 3306 is the default MySql port.
The value is ignored if Unix socket is used.

Use this to connect to a server in a replicated server configuration without concern on which server to use.

Use SSL if the server supports it, but allow connection in all cases

This option is available from Connector/NET version 6.2.1

Always use SSL. Deny connection if server does not support SSL.

This option is available from Connector/NET version 6.2.1

This option is available from Connector/NET version 6.2.1

This option is available from Connector/NET version 6.2.1

This option is available from Connector/NET version 6.2.1

This option is available from Connector/NET version 5.2.2

Returns a MySqlDateTime object for invalid values and a System.DateTime object for valid values

Returns System.DateTime.MinValue valued System.DateTime object for invalid values and a System.DateTime object for valid values.

The use of auto enlist transactionscope (default behaviour) could cause trouble in medium trust environments.

Default behaviour is that parameters for stored routines (stored procedures) are checked against the server

Some permissions and value casting related errors reported fixed when using this connection option.

The default behaviour is to read tables mysql.proc/INFORMATION_SCHEMA.ROUTINES and try to map provided command parameter values to the called procedures parameters and type cast values accordingly.
This can be troublesome if permissions to the (aforementioned) sproc info tables are insufficient.
The driver will not automatically map the parameters so you must manually set parameter types and you must also make sure to add the parameters to the command object in the exact order as appeared in the procedure definition.
This option is available from Connector/NET version 5.0.4

Specifying DefaultTableCacheAge is optional, default value is 60 seconds.
This option is available from Connector/NET version 6.4

This option is available from Connector/NET version 5.2.6

From version 6.2 idle connections are removed from the pool, freeing resources on the client (sockets) and the server (sockets and threads). Do not manually keep (global) connections and open close. Keep connection object creation and disposal as tight as possible, this might be counterintuitive but pooling mechanisms will take care of caching well and your code will be cleaner.

This is the default behaviour.

Default values are 0 and 100.

Makes an additional round trip to the server when obtaining a connection from the pool and connection state will be reset.

This is useful in load balancing scenarios when available servers change you don't want 100 constant connections in the pool pointing to only one server.

Specified in seconds, the amount of time after connection object creation the connection will be destroyed. Destruction will only happen when connections are returned to pool.

A connection might be long lived in the pool, however the connections server settings are updated (SHOW VARIABLES command) each time returned to the pool. This makes the client use of the connection object up to date with the correct server settings. However this causes a round trip and to optimize pooling performance this behaviour can be turned off.

This option is available from Connector/NET version 6.3

This option is available from Connector/NET version 6.4.4
The Windows Native Authentication Plugin must be installed for this to work.

Number of seconds between each keep-alive package send.

This option is available from Connector/NET version 6.1.1

The default is 25, meaning that stored procedure meta data (such as input/output data types etc) for the latest 25 called procedures will be cached in client memory.

This option is available from Connector/NET version 5.0.2

This enables Visual Studio wizards that bracket symbols with [] to work with Connector/Net. This option incurs a performance hit, so should only be used if necessary.

This option is available from Connector/NET version 6.3.1

Use this one to specify a default command timeout for the connection. Please note that the property in the connection string does not supercede the individual command timeout property on an individual command object.

This option is available from Connector/NET version 5.1.4.

Use this one to specify the length in seconds to wait for a server connection before terminating the attempt and receive an error.

Use this one to instruct the provider to ignore any command prepare statements and prevent corruption issues with server side prepared statements.

The option was added in Connector/NET version 5.0.3 and Connector/NET version 1.0.9.

Use this one to specify which network protocol to use for the connection.

"socket" is the default value used if the key isn't specified. Value "tcp" is an equivalent for "socket".

Use "pipe" to use a named pipes connection, "unix" for a Unix socket connection and "memory" to use MySQL shared memory.

It's possible to explicit set the shared memory object name used for communication.

It's possible to explicit set the pipe name used for communication, if not set, 'mysql' is the default value.

It is the port value of -1 that tells the driver to use named pipes network protocol. This is available on Windows only. The value is ignored if Unix socket is used.

It's possible to explicit set the shared memory object name used for communication.

Use this one to specify which character set to use to encode queries sent to the server.

Note! Use lower case value utf8 and not upper case UTF8 as this will fail.
Note that resultsets still are returned in the character set of the data returned.