I have a lmdb database and I'm trying to read its contents. The irony is nothing gets printed on screen. This is the code snippet that I have written for reading from lmdb:
import caffe
import lmdb
import numpy as np
from caffe.proto import caffe_pb2
import cv2
import sys
db_train = lmdb.open('mnist_train_lmdb')
db_train_txn = db_train.begin()
cursor = db_train_txn.cursor()
print db_train
print db_train_txn
print db_train_txn.cursor()
datum = caffe_pb2.Datum()
index = sys.argv[0]
size_train = 50000
size_test = 10000
data_train = np.zeros((size_train, 1, 28, 28))
label_train = np.zeros(size_train, dtype=int)
print 'Reading training data...'
i = -1
for key, value in cursor:
i = i + 1
if i % 1000 == 0:
print i
if i == size_train:
break
datum.ParseFromString(value)
label = datum.label
data = caffe.io.datum_to_array(datum)
data_train[i] = data
label_train[i] = label
This prints :
<Environment object at 0x0000000009CE3990>
<Transaction object at 0x0000000009CE1810>
<Cursor object at 0x0000000009863738>
Reading training data...
Reading test data...
It seems the for loop doesn't run at all. What am I missing here?
I checked and it seems this is the normal way of reading from lmdb, all source examples that I have seen have similar approach.
Correct myself:
Both way of using lmdb.Cursor()
for key, value in cursor:
and
while cursor.next():
are right and I was wrong in the original answer.
You didn't use cursor properly and a slight modification should be made in your code like:
... # original stuff
print 'Reading training data...'
i = -1
while cursor.next(): # Move to the next element, and
i = i + 1 # note cursor starts in an unpositioned state
if i % 1000 == 0:
print i
if i == size_train:
break
datum.ParseFromString(cursor.value())
label = datum.label
data = caffe.io.datum_to_array(datum)
data_train[i] = data
label_train[i] = label
For more usage about lmdb python binding, you can refer here.