Python Program Context Managers with (File) Experiments

Python Program Context managers with (file) – A context manager is a function that controls access to a resource and releases the resource when control returns to the calling context. The most common use of this facility is to manage resources such as files, network connections, and database connections.

A file is a sequence of bytes stored on a computer. A resource is anything that is used up by an operation. Python provides two facilities to manage resources:

With the statement: The with statement is used to open a resource. It is a compound statement consisting of two parts: the “with” clause, which specifies the resource to be opened, and the block containing the statement.

File object: A file object is created by the with statement and represents the resource that was opened. The file object has methods to read and write data to the opened file.

import: This statement is used to import modules into the interpreter. The import statement tells the interpreter to load and execute a module with statement:

Example #1:

import sys
import os
with open(os.path.join(sys.prefix, "lib", "test.txt"), 'w') as fp:
fp.write('This is a test file.')
fp.close()
print(os.listdir(os.path.join(sys.prefix, "lib")))
os.path.join:

Example# 2: 

import os
with open("myfile.txt", "w") as f:
print("My file has been created successfully")
print("The text that I am printing is ", end="")
f.write("This is a text that I am writing into my file")
os.remove("myfile.txt")
With open(file) as f:
print('File found')
print("File opened successfully")
print("text")
f.write("This is a text that I am writing into my file")
os.remove("myfile.txt")

Python File-Based Experiments

Experiments are useful in testing software. They are used to run experiments over a period of time to measure various metrics. In this article, I will explain how you can use Python’s context managers to create file-based experiments.

The with statement is one of the most important features of Python. A context manager is a special form of the with statement that provides a mechanism to access a resource.

Here, the resource is a file. The with statement creates a file object and uses it to access the resource. The resource is accessed when the context manager is first used.

Example# 3: 

We have a file called example.txt. We will write some data to the file and then read the data back.

data = open("example.txt", "w")
data.write("Hello")
data.close()
print(open("example.txt").read())

Let us analyze this example.

1. First, the open function is called with a filename argument as the first argument and the mode as the second argument. When we call open, it returns a file object.
2. Next, the file object is created using the context manager. The context manager provides an instance of the file object.
3. Finally, the file is opened using the file object returned by the context manager.
4. The with statement is used to create the file object.
5. The file is closed once the with statement is executed.
6. We then print the content of the file.

Example# 4:

with open('out.txt', 'w') as h:
h.write("hello\n")
h = open('out.txt')
print(h.read())
f = open('out.txt', 'w')
f.write("hello\n")
f.close()
# for line in open("myfile.txt"):
#	print line,
# the file is closed only when script ends