Python file string write

We also briefly explored the tell and seek methods to manipulate a file. Back to articles list Articles. Use write to Write to File in Python The first step to write a file in Python is to open it, which means you can access it through a script. We can then call the write method to modify our file programmatically.

We need to call the read method, as shown below: Open and read the file after writing: with open "file. We can modify our code with the following: open and write to file with open "file2. Use writerow for a Single Row To write in a CSV file, we need to open the file, create a writer object and update the file. Use tell to Get the Current Position The tell method can be used to get the current position of the file handle in the file. Use seek to Change Stream Positions The seek method is used to change the stream position.

The syntax is: fp. It can be a positive going forwards or negative going backwards number. It can be: 0: The beginning of the file. If you omit the whence parameter, the default value is 0. Tags: python python basics.

Work more efficiently with files and directories in Python. This course will make your daily work easier. How to Rename Files Python. Do you know how to rename, batch rename, move, and batch move files in Python? Discover how! It will improve your productivity. CSV files are one of the most popular file formats for data transfer.

See how easy it is to work with them in Python. Subscribe to our newsletter Join our monthly newsletter to be notified about the latest posts. Email address. If encoding is not specified, the default is platform dependent see open. Be very careful to use binary mode when reading and writing such files.

It is good practice to use the with keyword when dealing with file objects. The advantage is that the file is properly closed after its suite finishes, even if an exception is raised at some point. Using with is also much shorter than writing equivalent try - finally blocks:. Calling f. After a file object is closed, either by a with statement or by calling f. The rest of the examples in this section will assume that a file object called f has already been created.

Otherwise, at most size characters in text mode or size bytes in binary mode are read and returned. If the end of the file has been reached, f. This makes the return value unambiguous; if f. For reading lines from a file, you can loop over the file object. This is memory efficient, fast, and leads to simple code:. If you want to read all the lines of a file in a list you can also use list f or f.

Other types of objects need to be converted — either to a string in text mode or a bytes object in binary mode — before writing them:. The position is computed from adding offset to a reference point; the reference point is selected by the whence argument.

A whence value of 0 measures from the beginning of the file, 1 uses the current file position, and 2 uses the end of the file as the reference point. In text files those opened without a b in the mode string , only seeks relative to the beginning of the file are allowed the exception being seeking to the very file end with seek 0, 2 and the only valid offset values are those returned from the f.

Any other offset value produces undefined behaviour. File objects have some additional methods, such as isatty and truncate which are less frequently used; consult the Library Reference for a complete guide to file objects. Strings can easily be written to and read from a file. Numbers take a bit more effort, since the read method only returns strings, which will have to be passed to a function like int , which takes a string like '' and returns its numeric value When you want to save more complex data types like nested lists and dictionaries, parsing and serializing by hand becomes complicated.

Rather than having users constantly writing and debugging code to save complicated data types to files, Python allows you to use the popular data interchange format called JSON JavaScript Object Notation. The standard module called json can take Python data hierarchies, and convert them to string representations; this process is called serializing.

Reconstructing the data from the string representation is called deserializing. Between serializing and deserializing, the string representing the object may have been stored in a file or data, or sent over a network connection to some distant machine.

The JSON format is commonly used by modern applications to allow for data exchange. Many programmers are already familiar with it, which makes it a good choice for interoperability.

If you have an object x , you can view its JSON string representation with a simple line of code:. Another variant of the dumps function, called dump , simply serializes the object to a text file. So if f is a text file object opened for writing, we can do this:. To decode the object again, if f is a text file object which has been opened for reading:. Well, this can also be an advantage compared to the with statement.

Say, you have a big code file and you need to write stuff into a file in the beginning and at the end of the code. In this case, it would be even better to open the file once and pass it into a print function call in the beginning and at the end. Python closes all files automatically if the script terminates.

In my opinion, you can and must leverage knowledge about the implementation details of a Python language. Most people stating them do not close files all the time themselves.

Sure, you can also use a simple multi-line statement to cram everything into a single line of Python code:. You create the file object and write into it using only a single line. This is the shortest and most concise way to write stuff into a file.

Python programmers will improve their computer science skills with these useful one-liners.