How do I load more than one python object stored in the same DAT file?

Question

So, I'm still learning how to use pickle, and have a limited knowledge of it. This may be a beginner question... I created this placeholder class:

class Student:

  def __init__(self):
    self.__name = ""
    self.__regNum = 0
    self.__fullTime = True
 
  def getName(self):
    return self.__name
  
  def getRegNum(self):
    return self.__regNum
  
  def getFullTime(self):
    return self.__fullTime
    
  def setName(self,name):
    self.__name = name
  
  def setRegNum(self,num):
    self.__regNum = num
    
  def setFullTime(self,fullTime):
    self.__fullTime = bool(fullTime)

I created two test students:

student1 = Student()
student1.setName("Joe")
student1.setRegNum(2110)
student1.setFullTime(1)

student2 = Student()
student2.setName("Jess")
student2.setRegNum(5124)
student2.setFullTime(0)

dumpFile = open("student.DAT","wb")
pickle.dump(student1,dumpFile)
pickle.dump(student2,dumpFile)

dumpFile.close()

loadFile = open("student.DAT","rb")

but I don't know how to read both separately after loading the .dat file as separate objects.

I tried to use the with open("student.dat", 'rb') as input: that I've seen on the internet, but I have no clue what it does to understand why it's not working. I tried numpy.fromfile but I don't understand the outcome I get, and I've seen people use pandas but I don't know a thing. I can't really understand what the solutions are when I look it up, what should I do?

score 0 · Answer 1 · answered Oct 27 '21 at 10:52

I would suggest you to dump a list of objects into your .dat file and retrieve that later while loading.

dumpFile = open("student.DAT","wb")
pickle.dump([student1, student2], dumpFile)
dumpFile.close()

loadFile = open("student.DAT","rb")
data = pickle.load(loadFile)    #data now contains a list of the objects
loadFile.close()

Then you can just iterate through data to access each object separately.

As with the case of using with open, its easy to understand. In simple words, it ensures that you dont have to close your file after use. For example the same code can be written as:

with open("student.DAT","wb") as dumpFile:
    pickle.dump([student1, student2], dumpFile)

with open("student.DAT","rb") as loadFile:
    data = pickle.load(loadFile)

How do I load more than one python object stored in the same DAT file?

1 Answers1