Php
DB MODULE
p252 ! Many databases are like dictionaries (map keys to values). The difference is that the database is on disk.
CodeCopy
import dbm
db = dbm.open('images', 'c')
db['myimage.jpg'] = '/images/myimage.jpg'
db['myimage.png'] = '/images/myimage.png'
print(db['myimage.jpg'])
# b'/images/myimage.jpg'
# the result is a bytes object (it begins with b)
db.close()
CodeCopy
import dbm
db = dbm.open('images_db')
for key in db.keys():
print(key, db[key])
# b'myimage.png' b'/images/myimage.png'
# b'myimage.jpg' b'/images/myimage.jpg'
db.close()
... 7 lines˄˄˄Pickling
! A limitation of db is that it works only with strings or bytes. With pickle module you can store any type. CodeCopy
import dbm
import pickle
# write
db = dbm.open('images_db', 'w')
t = [1, 2, 3]
s = pickle.dumps(t) # b'\x80\x03]q\x00(K\x01K\x02K\x03e.'
db['mylist'] = s
db.close()
# read
db = dbm.open('images_db')
b = db['mylist']
s = pickle.loads(b)
print(s) # [1, 2, 3]
db.close()
... 14 lines˄˄˄ CodeCopy
import pickle
t1 = (1, 2, 3)
s = pickle.dumps(t1)
t2 = pickle.loads(s)
print(t2) # (1, 2, 3)
print(t1 == t2) # True
print(t1 is t2) # False
... 7 lines˄˄˄Shelve
In a 'shelf' db the values can be any objects that pickle can handle. CodeCopy
import shelve
t = (1, 2, 3)
db = shelve.open("images_db", 'w')
db['my_tuple'] = t
db.close()
db = shelve.open("images_db", 'w')
assert db['my_tuple'] == (1, 2, 3) # pass
db.close()
... 8 lines˄˄˄➥ Questions
CARD
22
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