How to save file in python

Saving Text, JSON, and CSV to a File in Python

Saving data to a file is one of the most common programming tasks you may come across in your developer life.

Python allows us to save files of various types without having to use third-party libraries. In this article, we’ll dive into saving the most common file formats in Python.

Opening and Closing a File

Opening a File

The contents of a file can be accessed when it’s opened, and it’s no longer available for reading and writing after it’s been closed.

Opening a file is simple in Python:

Here are some of the commonly used ones:

Let’s say you wanted to write to a file and then read it after, your mode should be ‘w+’. If you wanted to write and then read from a file, without deleting the previous contents then you’ll use ‘a+’.

Closing a File

Closing a file is even easier in Python:

You simply need to call the close method on the file object. It’s important to close the file after you are finished using it, and there are many good reasons to do so:

For small scripts, these aren’t pressing concerns, and some Python implementations will actually automatically close files for you, but for large programs don’t leave closing your files to chance and make sure to free up the used resources.

Using the «with» Keyword

Closing a file can be easily forgotten, we’re human after all. Lucky for us, Python has a mechanism to use a file and automatically close it when we’re done.

To do this, we simply need to use the with keyword:

The file will be open for all the code that’s indented after using the with keyword, marked as the # TODO comment. Once that block of code is complete, the file will be automatically closed.

This is the recommended way to open and write to a file as you don’t have to manually close it to free up resources and it offers a failsafe mechanism to keep your mind on the more important aspects of programming.

Saving a Text File

Now that we know the best way to access a file, let’s get straight into writing data.

Fortunately, Python makes this straightforward as well:

The write() function takes a string and puts that content into the file stream. Although we don’t store it, the write() function returns the number of characters it just entered i.e. the length of the input string.

Saving Multiple Lines at Once

With the write() function we can take one string and put it into a file. What if we wanted to write multiple lines at once?

We can use the writelines() function to put data in a sequence (like a list or tuple) and into a file:

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As before, if we want the data to appear in new lines we include the newline character at the end of each string.

If you’d like to skip the step of manually entering the newline character after each item in the list, it’s easy to automate it:

Saving a CSV File

CSV (Comma Separated Values) files are commonly used for storing tabular data. Because of its popularity, Python has some built-in methods to make writing files of that type easier:

This object provides us with the writerow() method which allows us to put all the row’s data in the file in one go.

If you’d like to learn more about using CSV files in Python in more detail, you can read more here: Reading and Writing CSV Files in Python.

Saving a JSON File

JSON is another popular format for storing data, and just like with CSVs, Python has made it dead simple to write your dictionary data into JSON files:

We do need to import the json library and open the file. To actually write the data to the file, we just call the dump() function, giving it our data dictionary and the file object.

If you’d like to know more about using JSON files in Python, you can more from this article: Reading and Writing JSON to a File in Python.

Conclusion

Saving files can come in handy in many kinds of programs we write. To write a file in Python, we first need to open the file and make sure we close it later.

It’s best to use the with keyword so files are automatically closed when we’re done writing to them.

We can use the write() method to put the contents of a string into a file or use writelines() if we have a sequence of text to put into the file.

For CSV and JSON data, we can use special functions that Python provides to write data to a file once the file is open.

Python Save to file

I would like to save a string to a file with a python program named Failed.py

Here is what I have so far:

5 Answers 5

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Here is a more pythonic version, which automatically closes the file, even if there was an exception in the wrapped block:

Naturally you may want to include newlines or other formatting in your output, but the basics are as above.

The same issue with closing your file applies to the reading code. That should look like this:

You can use this function:

We need to be careful with the w mode, as it will overwrite into the file if it already exists. Due to this, all the previous data are erased.

Writing a string or sequence of bytes (for binary files) is done using the write() method. This method returns the number of characters written to the file.

This program will create a new file named Failed.py in the current directory if it does not exist. If it does exist, it is overwritten.

We must include the newline characters ourselves to distinguish the different lines.

Python: how do I save a file in a different directory?

How could I save it in a new directory without switching directories? I would want to save the files in a directory like Pics2/forcing3damping3omega3set2.png.

3 Answers 3

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By using a full or relative path. You are specifying just a filename, with no path, and that means that it’ll be saved in the current directory.

To save the file in the Pics2 directory, relative from the current directory, use:

or better still, construct the path with os.path.join() and string formatting:

Best is to use an absolute path:

You can join your filename with a full path so that it saves in a specific location instead of the current directory:

Using os.path.join will properly handle the separators, in a platform independent way.

I am assuming that you are working with pylab ( matplotlib ).

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How to save python screen output to a text file

I’d like to query items from a dict and save the printed output to a text file.

Here’s what I have:

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Let me summarize all the answers and add some more.

To write to a file from within your script, user file I/O tools that are provided by Python (this is the f=open(‘file.txt’, ‘w’) stuff.

If don’t want to modify your program, you can use stream redirection (both on windows and on Unix-like systems). This is the python myscript > output.txt stuff.

If you want to see the output both on your screen and in a log file, and if you are on Unix, and you don’t want to modify your program, you may use the tee command (windows version also exists, but I have never used it)

A quick and dirty hack to do this within the script is to direct the screen output to a file:

and then reverting back to outputting to screen at the end of your code:

This should work for a simple code, but for a complex code there are other more formal ways of doing it such as using Python logging.

abarnert ‘s answer is very good and pythonic. Another completely different route (not in python) is to let bash do this for you:

This works in general to put all the output of a cli program (python, perl, php, java, binary, or whatever) into a file, see How to save entire output of bash script to file for more.

If you want the output to go to stdout and to the file, you can use tee:

100ft from one of the creators of tcsh so I definitely should have known better. I’ve updated to reflect your info.

What you’re asking for isn’t impossible, but it’s probably not what you actually want.

Instead of trying to save the screen output to a file, just write the output to a file instead of to the screen.

Just add that >>outfile into all your print statements, and make sure everything is indented under that with statement.

More generally, it’s better to use string formatting rather than magic print commas, which means you can use the write function instead. For example:

But if print is already doing what you want as far as formatting goes, you can stick with it for now.

What if you’ve got some Python script someone else wrote (or, worse, a compiled C program that you don’t have the source to) and can’t make this change? Then the answer is to wrap it in another script that captures its output, with the subprocess module. Again, you probably don’t want that, but if you do:

Best Ways to Save Data in Python

Hello readers! In this tutorial, we’ll be dealing with how we can effectively save data in Python.

How to Save Data in Python?

When we’re working on Python applications, we’ll be dealing with Python objects directly, since everything is an object in Python. Let’s look at some ways by which we can store them easily!

1. Using Pickle to store Python Objects

If we want to keep things simple, we can use the pickle module, which is a part of the standard library to save data in Python.

We can “pickle” Python objects to a pickle file, which we can use to save/load data.

So if you have a custom object which you might need to store / retrieve, you can use this format:

To load the same object back again, we could use pickle.load() using similar logic.

We’ve just retrieved our old data successfully!

2. Using Sqlite3 to save data in Python persistently

If you want to use a persistent database to save data in Python, you can use the sqlite3 library which provides you APIs for using Sqlite databases.

Again, this is a part of the standard library, so there’s no need to pip install anything!

You’d have to serialize and de-serialize them to their appropriate Database types.

To look at some examples, you can refer to this article on using sqlite in Python.

3. Using SqliteDict as a persistent cache

If you find using sqlite3 too tedious, there’s a much better solution! You can use sqlitedict for storing persistent data, and this internally uses an sqlite3 database to handle the storage.

You have to install this package using pip:

The only thing you need to keep in mind is that you need to use key:value mappings to store / retrieve data, just like a dictionary!

Here’s a very simple example using the MyClass instance.

Indeed, we’ve just loaded our Python object successfully! If you notice, sqlitedict will create a database cache.sqlite3 automatically, if it doesn’t exist, and then use it to store / load data.

Conclusion

In this article, we looked at how we can use Python to store data in different ways.