![]() ![]() Thus the modes for opening a file should be: + is optionally added, U should be avoided.Īs I found out the hard way, it is a good idea to always specify t when opening a file in text mode since r is an alias for rt in the standard open() function but an alias for rb in the open() functions of all compression modules (when e.g. The modes r, w, x, a are combined with the mode modifiers b or t. 'U' universal newlines mode (for backwards compatibility should not be used in new code) '+' open a disk file for updating (reading and writing) 'a' open for writing, appending to the end of the file if it exists 'x' open for exclusive creation, failing if the file already exists 'w' open for writing, truncating the file first ![]() The Python 3 opening modes are: 'r' open for reading (default) I find it important to note that python 3 defines the opening modes differently to the answers here that were correct for Python 2. Write('aa') seek(0, 0) read(2) write('b') - second write raises IOError ![]() Write('aa') seek(0, 0) read(1) write('b') - second write is ignored interesting behavior at least on my win7 / python2.7, for new file opened in a+ mode: Note: a and a+ always append to the end of file - ignores any seek movements.īTW. Position at end - after file is opened, initial position is set to the end of the file Position at start - after file is opened, initial position is set to the start of the file Truncate - during opening of the file it is made empty (all content of the file is erased) |-Ĭreate - file is created if it does not exist yet Same info, just in table form | r r+ w w+ a a+ Quent writes to the file will always end up at the then currentĮnd of file, irrespective of any intervening fseek(3) or similar. The stream is positioned at the end of the file. Irrespective of any intervening fseek(3) or similar. To the file will always end up at the then current end of file, Stream is positioned at the end of the file. The file is created if it does not exist. The file is created if it does notĮxist, otherwise it is truncated. The stream is positioned at the beginning of the file. ``w'' Truncate file to zero length or create text file for writing. Sequences (Additional characters may follow these sequences.): The BSD fopen manpage defines them as follows: The argument mode points to a string beginning with one of the following The data being written will be inserted at the end, after the existing data.The opening modes are exactly the same as those for the C standard library function fopen(). The handle is positioned at the end of the file. Append and Read (‘a+’): Open the file for reading and writing.The data being written will be inserted at the end, after the existing data. Append Only (‘a’): Open the file for writing.The handle is positioned at the beginning of the file. For existing files, data is truncated and over-written. Write and Read (‘w+’): Open the file for reading and writing.Creates the file if the file does not exist. ![]() For the existing files, the data is truncated and over-written.
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