Python 3 file i o

Dictionaries in Python. Popular Examples Add two numbers. Check prime number. Find the factorial of a number. Print the Fibonacci sequence. Check leap year. Reference Materials Built-in Functions. List Methods. Dictionary Methods. String Methods. Start Learning Python. Explore Python Examples. Related Topics Python open. Working with CSV files in Python. How to Get Started With Python? Video: Reading and Writing Files in Python.

Files Files are named locations on disk to store related information. Hence, in Python, a file operation takes place in the following order: Open a file Read or write perform operation Close the file Opening Files in Python Python has a built-in open function to open a file.

The default is reading in text mode. In this mode, we get strings when reading from the file. Mode Description r Opens a file for reading. Creates a new file if it does not exist or truncates the file if it exists. If the file already exists, the operation fails.

Creates a new file if it does not exist. Method Description close Closes an opened file. It has no effect if the file is already closed. Reads till end of file if it is negative or None.

Reads in at most n bytes if specified. If size is not specified, resizes to current location. Previous Tutorial:. Next Tutorial:. Share on:. However, many developers forget to specify the encoding when opening text files encoded in UTF-8 e. This causes bugs because the locale encoding is not UTF-8 for most Windows users.

For example:. Additionally, while there is no concrete plan as of yet, Python may change the default text file encoding to UTF-8 in the future. Accordingly, it is highly recommended that you specify the encoding explicitly when opening text files. When you need to run existing code on Windows that attempts to open UTF-8 files using the default locale encoding, you can enable the UTF-8 mode.

See UTF-8 mode on Windows. New in version 3. However, please consider using UTF-8 by default i. This is an alias for the builtin open function. This function raises an auditing event open with arguments path , mode and flags. The mode and flags arguments may have been modified or inferred from the original call. Opens the provided file with mode 'rb'.

This function should be used when the intent is to treat the contents as executable code. Overriding the behavior is intended for additional validation or preprocessing of the file.

This function returns encoding if it is not None and "locale" if encoding is None. This function emits an EncodingWarning if sys. See Text Encoding for more information. This is a compatibility alias for the builtin BlockingIOError exception. An exception inheriting OSError and ValueError that is raised when an unsupported operation is called on a stream.

First abstract base classes ABCs , which are used to specify the various categories of streams, then concrete classes providing the standard stream implementations. The abstract base classes also provide default implementations of some methods in order to help implementation of concrete stream classes. For example, BufferedIOBase provides unoptimized implementations of readinto and readline. It defines the basic interface to a stream.

Note, however, that there is no separation between reading and writing to streams; implementations are allowed to raise UnsupportedOperation if they do not support a given operation. It deals with the reading and writing of bytes to a stream. It deals with buffering on a raw binary stream RawIOBase. Its subclasses, BufferedWriter , BufferedReader , and BufferedRWPair buffer raw binary streams that are readable, writable, and both readable and writable, respectively.

BufferedRandom provides a buffered interface to seekable streams. It deals with streams whose bytes represent text, and handles encoding and decoding to and from strings. Finally, StringIO is an in-memory stream for text. Argument names are not part of the specification, and only the arguments of open are intended to be used as keyword arguments. The following table summarizes the ABCs provided by the io module:.

Inherited IOBase methods, read , and readall. Inherited IOBase methods, readinto , and readinto1. Inherited IOBase methods, encoding , errors , and newlines. There is no public constructor. This class provides empty abstract implementations for many methods that derived classes can override selectively; the default implementations represent a file that cannot be read, written or seeked.

Even though IOBase does not declare read or write because their signatures will vary, implementations and clients should consider those methods part of the interface. Also, implementations may raise a ValueError or UnsupportedOperation when operations they do not support are called. The basic type used for binary data read from or written to a file is bytes. Other bytes-like objects are accepted as method arguments too. Note that calling any method even inquiries on a closed stream is undefined.

Implementations may raise ValueError in this case. IOBase and its subclasses supports the iterator protocol, meaning that an IOBase object can be iterated over yielding the lines in a stream. Lines are defined slightly differently depending on whether the stream is a binary stream yielding bytes , or a text stream yielding character strings.

See readline below. IOBase is also a context manager and therefore supports the with statement. IOBase provides these data attributes and methods:. Flush and close this stream. This method has no effect if the file is already closed. Once the file is closed, any operation on the file e. As a convenience, it is allowed to call this method more than once; only the first call, however, will have an effect. True if the stream is closed. Return the underlying file descriptor an integer of the stream if it exists.

Flush the write buffers of the stream if applicable. This does nothing for read-only and non-blocking streams. Return True if the stream is interactive i. Return True if the stream can be read from. If False , read will raise OSError. Read and return one line from the stream. If size is specified, at most size bytes will be read. Read and return a list of lines from the stream. Change the stream position to the given byte offset. Values for whence are:.

The valid values for a file could depend on it being open in text or binary mode. Return True if the stream supports random access. If False , seek , tell and truncate will raise OSError. Resize the stream to the given size in bytes or the current position if size is not specified. This resizing can extend or reduce the current file size. In case of extension, the contents of the new file area depend on the platform on most systems, additional bytes are zero-filled. The new file size is returned.

Return True if the stream supports writing. If False , write and truncate will raise OSError. Write a list of lines to the stream. Line separators are not added, so it is usual for each of the lines provided to have a line separator at the end. Prepare for object destruction. Base class for raw binary streams. It inherits IOBase.

Opens a file for reading only in binary format. Opens a file for both reading and writing in binary format. The file pointer placed at the beginning of the file. Opens a file for writing only. Overwrites the file if the file exists. If the file does not exist, creates a new file for writing.

Opens a file for writing only in binary format. Opens a file for both writing and reading. Overwrites the existing file if the file exists.

If the file does not exist, creates a new file for reading and writing. Opens a file for both writing and reading in binary format. Opens a file for appending.

The file pointer is at the end of the file if the file exists. That is, the file is in the append mode. If the file does not exist, it creates a new file for writing. Opens a file for appending in binary format. Opens a file for both appending and reading. The file opens in the append mode. If the file does not exist, it creates a new file for reading and writing. Opens a file for both appending and reading in binary format. Once a file is opened and you have one file object, you can get various information related to that file.

The close method of a file object flushes any unwritten information and closes the file object, after which no more writing can be done.

Python automatically closes a file when the reference object of a file is reassigned to another file. It is a good practice to use the close method to close a file. The file object provides a set of access methods to make our lives easier.

We would see how to use read and write methods to read and write files. The write method writes any string to an open file. It is important to note that Python strings can have binary data and not just text.