This paper will seek to demonstrate file management in python with particular attention to reading, writing and file appending. It will explain steps necessary to read the content of a file, to change its content and to add contents to a file without deleting its previous contents.
Concepts Introduction
File management functionality in python starts by opening a file, performing the required activity on the file such as appending or modifying the file and then shutting the file. The files are affixed off the program in most cases within the disk storage and in performing such functions python provides syntax for inputting them into the program using open command.Opening any existing file requires the same two basic attributes; its title and the appropriate mode. The mode controls the intended action for that particular file to be carried out. There are three basic modes of operation.
The most common modes are:
- `'r'` for reading The file is available for reading, should the file not exist an error is returned.
- `'w'` for writing This mode is often used when a new document must be created. If a document with the same name exists, it will be deleted and replaced by this one.
- `'a'` for appending This mode is used when existing documents must be updated rather than replaced. It simply creates a new document if none are found with the same name. Existing documents remain intact and the new information is added at the end of such documents.
Reading from a File
When the file's content is required, it can be simply opened in read mode (`'r'`), numerous other methods are available in python as well. All of these methods are file handling solutions.The `read()` function extracts data from the file and returns it as one single large chunk of text. There's more: if you only want to read 'n' characters from that file, you would just call `read(n)` where 'n' would be the number of characters to be read.
In order to read a file, line by line, `readline()` would be helpful, this method reads an individual line of text inside the file. Another method is `readlines()`, which reads all lines in a file and returns them as an array of strings in which each element of the array represents a line inside the file.
If you don't want to use a file anymore, then you should properly close it by calling the `close()` method on the file object. This makes sure that all the resources are freed and the file is safely closed.
Writing to a File
In python, files can be written to by opening the file in write mode ('w'). This means that all previous content of the file can either be erased or if the file doesn't exist, then a new file is created.The `write()` method allows you to store a variable string in a file. In order to save in, say, a notepad, you can invoke the `write()` function many times or employ the `writelines()` method which is capable of writing every line of a list in one go.
It is critical to understand that when you open a file in write mode, the content that exists therein is completely removed. If, however, you only wish to add new data and keep the prior data intact, you have to select the file in append mode.
Adding More Content to The File
You can add more information to a certain file if you select the appropriate file in append mode. This mode is also much like write mode, except rather than erasing the previous content of the file, it saves its content in an unused space to the furthest end of the document.When attaching new information within an existing document, the content currently inside the document cannot be removed or over-written, and so it must be kept in mind. Attachments take place without any influence on the current content of the file.
In order to add more content to any file, you may use the 'write() function, just as you would use for any other writing task but note this time that the content is saved inside the file in append mode so all new content will always be saved at the end of the file.
File Handling with the help of Context Managers
You can control your files by opening and closing them via their respective methods `open()` and `close()`, however it is best practice to utilize a context manager. Whenever delving into file operations in Python, a context manager is an instance that handles the functionality for you by opening and closing files as required without the need for you to do it manually.The common practice of file handling using context managers is through the use of a 'with' statement. Once a file is opened with 'with', Python takes care of the closing even if the operation encounters an error. This also lowers the chances of a user ending up with an unclosed file and toppers the needed management of the resources.
Here's a basic example of how to read from a file using the `with` statement:
File Reading with Context Manager Example
with open('example.txt', 'r') as file:
content = file.read()
print(content) File Read related Errors
When dealing with files, one should always be prepared to meet the errors and problems that the operations can encounter. Such as, an already missing file which is required for one to open, or a missing file permission.Python has exception handling for this purpose. And there are `try` and `except` blocks for that too. Here's an example:
File Error Handling Example
try:
with open('example.txt', 'r') as file:
content = file.read()
print(content)
except FileNotFoundError:
print("The file does not exist.") 
