Python Common libraries

Sqlite3

• Create a Connection object to represent a db with the following code:

Import Sqlite3 conn = Sqlite3.connect (' example.db ') #如果要在RAM中创建一个db, DB name used: Memory:

When more than one connection accesses the db at the same time and there is a process that modifies the DB, the DB is always locked until transaction is committed, and the common parameters of Connect () are:

• The timeout parameter specifies how long the connection waits and then throws an exception, which defaults to 5 seconds.
• Isolation_level: Set How to turn on Tranction, open transaction when a DML statement is encountered by default, submit when NON-DML statement is encountered transaction
• Cached_statements: The number of statements that this connection can hold in the cache, which defaults to 100
• Type Uri:boolean, specifying the db with a URI, you can specify the option of the connection, such as opening the DB as read-only
  db = Sqlite3.connect (' File:path/to/database?mode=ro ', uri=true)
  

• then create a cursor object to execute the SQL command when executing the query, pay attention to the security of the SQL statement,
  

  C=conn.cursor () # never do this--insecure! Symbol = ' Rhat ' C.execute ("SELECT * from stocks WHERE symbol = '%s '"% symbol) ? # do this instead, note that there is only one element in a tuple followed by a comma #sql语句中的替换符为? t = (' Rhat ',) C.execute (' SELECT * from stocks WHERE symbol=? ', T) Print (C.fetchone ()) ? # Larger example that inserts many records at a time purchases = [(' 2006-03-28 ', ' BUY ', ' IBM ', 1000, 45.00), (' 2006-04-05 ', ' BUY ', ' MSFT ', 1000, 72.00), (' 2006-04-06 ', ' SELL ', ' IBM ', 500, 53.00), ] C.executemany (' INSERT into stocks VALUES (?,?,?,?,?) ', purchases)

• If you finish executing the query statement using execute, you can use the following methods to get the data:
  • Use the cursor as a iterator to get one row of row data at a time using the For statement
  • Use Fetchone () to fetch one row of row data at a time, and finally return none
  • Use Fetchall () to get the list of row, no data to return none
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Python Common libraries