标签：pen effective bin object over line this code asp
This tutorial shows you how to work with MySQL BLOB data in Python, with examples of updating and reading BLOB data.
The authors table has a column named photo whose data type is BLOB. We will read data from a picture file and update to the photo column.
First, we develop a function named read_file() that reads a file and returns the file’s content:
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def read_file(filename):
with open(filename, ‘rb‘) as f:
photo = f.read()
return photo
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Second, we create a new function named update_blob() that updates photo for an author specified by author_id .
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from mysql.connector import MySQLConnection, Error
from python_mysql_dbconfig import read_db_config
def update_blob(author_id, filename):
# read file
data = read_file(filename)
# prepare update query and data
query = "UPDATE authors " \
"SET photo = %s " \
"WHERE id = %s"
args = (data, author_id)
db_config = read_db_config()
try:
conn = MySQLConnection(**db_config)
cursor = conn.cursor()
cursor.execute(query, args)
conn.commit()
except Error as e:
print(e)
finally:
cursor.close()
conn.close()
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Let’s examine the code in detail:
read_file() function to read data from a file and return it.author_id . The args variable is a tuple that contains file data andauthor_id . We will pass this variable to the execute() method together with the query .try except block, we connect to the database, instantiate a cursor, and execute the query with args . To make the change effective, we call commit() method of the MySQLConnection object.finally block.Notice that we imported MySQLConnection and Error objects from the MySQL Connector/Python package and read_db_config() function from the python_mysql_dbconfig module that we developed in the previous tutorial.
Let’s test the update_blob() function.
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def main():
update_blob(144, "pictures\garth_stein.jpg")
if __name__ == ‘__main__‘:
main()
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Notice that you can use the following photo and put it into the pictures folder for testing.
Inside the main function, we call the update_blob() function to update the photo column for the author with id 144. To verify the result, we select data from the authors table.
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SELECT * FROM authors
WHERE id = 144;
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It works as expected.
In this example, we select BLOB data from the authors table and write it into a file.
First, we develop a write_file() function that write a binary data into a file as follows:
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def write_file(data, filename):
with open(filename, ‘wb‘) as f:
f.write(data)
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Second, we create a new function named read_blob() as below:
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def read_blob(author_id, filename):
# select photo column of a specific author
query = "SELECT photo FROM authors WHERE id = %s"
# read database configuration
db_config = read_db_config()
try:
# query blob data form the authors table
conn = MySQLConnection(**db_config)
cursor = conn.cursor()
cursor.execute(query, (author_id,))
photo = cursor.fetchone()[0]
# write blob data into a file
write_file(photo, filename)
except Error as e:
print(e)
finally:
cursor.close()
conn.close()
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The read_blob() function reads BLOB data from the authors table and write it into a file specified by the filename parameter.
The code is straightforward:
read_db_config() function.try except block, we connect to the database, instantiate cursor, and execute the query. Once we got the BLOB data, we use the write_file() function to write it into a file specified by the filename .Now, let’s test the read_blob() function.
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def main():
read_blob(144,"output\garth_stein.jpg")
if __name__ == ‘__main__‘:
main()
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If you open the output folder in the project and see a picture there, it means that you have successfully read the blob from the database.
标签：pen effective bin object over line this code asp
原文地址：http://www.cnblogs.com/hushaojun/p/6223505.html
