Intern study summary - Jul 11 Tue

Python

Equal and ==

self.assertEqual is a method provided by the unittest module in Python. It is used in test cases to assert that two values are equal. If they are not, the test fails and an AssertionError is raised.

self.assertEqual uses the == operator to check for equality, which checks if two objects have the same value. This can be thought of as checking equality "by value".

In Python, == compares the value of two objects, whereas the is operator checks whether they are the exact same object (i.e., comparing "by reference"). For instance:

a = [1, 2, 3]
b = [1, 2, 3]
c = a

print(a == b)  # True - a and b have the same values
print(a is b)  # False - a and b are different objects in memory
print(a is c)  # True - a and c are the exact same object in memory

compare with Java

In Java, the == operator checks for reference equality (whether two variables reference the exact same object), which is analogous to the is operator in Python. The equals method in Java is used to check for value equality, but its behavior can vary depending on how it's implemented in the class of the objects being compared. This is most similar to the == operator in Python or self.assertEqual in Python's unittest module.

Return two different type together

example:

If I have return as return model, target_size, model is Model type, and target_size is ndarray type. How do I put in the function after >?

The "->" symbol is used in Python type hinting to indicate the return type of a function. It's used to make the code easier to understand and maintain, and to help in using tools that perform type checking or provide coding assistance.

In your case, since your function is returning a tuple of a Model type object and a ndarray type object, you can indicate the return type like this:

from keras.models import Model
import numpy as np

def your_function(...) -> tuple[Model, np.ndarray]:
    # your code
    return model, target_size

In this code:

• Model is the type for the model.
• np.ndarray is the type for target_size.

Note that these type hints are not enforced at runtime. Python is still a dynamically typed language. These hints are primarily for the benefit of the programmer and development tools.

Also, if your Python version is lower than 3.9, you might want to use Tuple from typing module because the built-in tuple does not support type hints in those versions:

from keras.models import Model
import numpy as np
from typing import Tuple

def your_function(...) -> Tuple[Model, np.ndarray]:
    # your code
    return model, target_size

Database

MongoDB Read by ID

In order to access MongoDB data in Python, you need to use a library called pymongo. Here's a simple example of how you can retrieve a document by its _id:

Firstly, install the pymongo package using pip:

pip install pymongo

And then use this script:

from pymongo import MongoClient
from bson.objectid import ObjectId

# Create a client connection to your MongoDB instance
client = MongoClient('mongodb://localhost:27017/')

# Access the 'database' database and the 'collection' collection
db = client['database']
collection = db['collection']

# Define the id you're looking for
id_to_find = '60ebe5ab9d6965cb97f9d0a2'  # replace with your id string

# Use the ObjectId class to convert the id string into an ObjectId
id_to_find = ObjectId(id_to_find)

# Use the find_one method, which returns the first matching document
document = collection.find_one({'_id': id_to_find})

# Print the document
print(document)

You will need to replace 'mongodb://localhost:27017/' with the connection string for your own MongoDB instance. Replace 'database' and 'collection' with the names of your database and collection, and '60ebe5ab9d6965cb97f9d0a2' with the id string of the document you're trying to find.

This script first connects to your MongoDB instance and selects the desired database and collection. It then uses the find_one method on the collection to retrieve the document with the specified _id. The find_one method returns None if no document matches the query. Finally, it prints out the document.

Remember to import the ObjectId class from the bson.objectid module, which is needed to convert the string representation of an id into a proper MongoDB ObjectId.