Strengthen your foundations with the Python Programming Foundation Course and learn the basics. Next Python - Copy contents of one file to another file. Recommended Articles. Article Contributed By :. Easy Normal Medium Hard Expert. Writing code in comment? Please use ide.
Load Comments. Connect and share knowledge within a single location that is structured and easy to search. I'm writing a program that finds certain lines of text in a file and writes them to another file to get rid of all the annoying text in between it's a.
Through my skills of python and googleing I have writen the following program. The program is working fine, but for the "subject" I want to tell the program to write not just the single line of text where the keyword "subject" is, but until it reaches a certain keyword in my case that is "END:VBODY".
What should I do? If you just need this one particular case, you can walk away with simple state variable. Something like this:. Here is another working solution just by adding a while loop under the if "Subject" in line condition.
How are we doing? Please help us improve Stack Overflow. Take our short survey. It takes two arguments, as shown below:.
The first argument is the name or path of the file including file name. And the second parameter optional represents a mode to open the file. The default value is the READ only mode. It is optional to pass the mode argument. It means that Python will open a file for read-only purpose. Python provides two functions to write into a text file: Write and Writelines.
This function puts the given text in a single line. You can check its syntax below:. You also need to know how to append the new text to an existing file. Whenever you open a file using one of these modes, the file offset is set to the EOF.
So, you can write the new content or text next to the existing content. Let's see them in detail. The "a" mode allows you to open a file to append some content to it.
And we want to add a new line to it, we can open it using the "a" mode append and then, call the write method, passing the content that we want to append as argument. This is the basic syntax to call the write method:. Sometimes, you may want to delete the content of a file and replace it entirely with new content.
You can do this with the write method if you open the file with the "w" mode. As you can see, opening a file with the "w" mode and then writing to it replaces the existing content. If you want to write several lines at once, you can use the writelines method, which takes a list of strings. Each string represents a line to be added to the file. Now you know how to create, read, and write to a file, but what if you want to do more than one thing in the same program?
Let's see what happens if we try to do this with the modes that you have learned so far:. How can we solve this? Very useful, right? This is probably what you will use in your programs, but be sure to include only the modes that you need to avoid potential bugs.
To remove a file using Python, you need to import a module called os which contains functions that interact with your operating system.
Particularly, you need the remove function. This function takes the path to the file as argument and deletes the file automatically.
Context Managers are Python constructs that will make your life much easier. By using them, you don't need to remember to close a file at the end of your program and you have access to the file in the particular part of the program that you choose. If the code is not indented, it will not be considered part of the context manager. This context manager opens the names. This variable is used in the body of the context manager to refer to the file object.
After the body has been completed, the file is automatically closed, so it can't be read without opening it again. But wait! We have a line that tries to read it again, right here below:. This error is thrown because we are trying to read a closed file. Awesome, right? The context manager does all the heavy work for us, it is readable, and concise.
When you're working with files, errors can occur. Sometimes you may not have the necessary permissions to modify or access a file, or a file might not even exist. As a programmer, you need to foresee these circumstances and handle them in your program to avoid sudden crashes that could definitely affect the user experience. Let's see some of the most common exceptions runtime errors that you might find when you work with files:. According to the Python Documentation , this exception is:.
For example, if the file that you're trying to open doesn't exist in your current working directory:. This is a huge advantage during the process of debugging. This is another common exception when working with files.
This exception is raised when you are trying to read or modify a file that don't have permission to access.
0コメント