• Sometimes you are given files and you have to read them.
  • We need to manage whether we are reading a contents of a file or making changes to it and writing to it.
    • This is due to if two applications are writing to a file at the same time.
  • Reading Files. In the example below, the file will be opened in read mode. 
    f = open('10_01_file.txt', 'r')
print(f)
  • The output is a file object: ```
<_io.TextIOWrapper name="10_01_file.txt" mode="r" encoding="UTF-8"> ``` * To get the text inside the file, we do: ``` # This reads the lines of the file one at a time. Every time this is run, a different file is displayed. The file object contains bookmarks of the files it has already read. It is possible to place this in a loop to read all lines of a file, however, we can do: f.readline() ``` ``` # This reads all of the lines of the file. It gets all the lines of the file that have not been read already and places them into a list of strings. f.readlines() ``` * provides the following output as an example: ``` Complex is better than complicated \n ``` * We can also perform it this way as well: ``` f = open('10_01_file.txt', 'r') for line in f.readlines(): print(line) ``` * All of the lines will be output double spaced. * That is because each line has a newline character at the end of it. * Remember, the `print` statement also includes new lines as well. * We can remove any leading or separate spaces/white lines with: ``` f = open('10_01_file.txt', 'r') for line in f.readlines(): print(line.strip()) ``` * The output for that would be; ``` Beautiful is better than ugly. Hot is better than not. etc ``` * Writing Files * We do this for example with: ``` f = open('10_01_output.txt', 'w') print(f) ``` * Once the above is ran, a file will be created. ``` f.write('Line 1') f.write('Line 2') ``` * The output for example is `6.` * Writing to files is a generally expensive operation. It only writes to the buffer when the buffer becomes full. * We can close the file with `f.close()` * A newline character is not printed between the lines. * To add this we can do: ``` f.write('Line 1\n') f.write('Line 2\n') ``` * If it is the same file that is written to, Python will overwrite the existing data in that file. * Appending Files * To continue to add additional data to a file, we can open that file in `append mode` ``` f = open('10_01_output.txt', 'a') f.write('Line 3\n') f.write('Line 4\n') # This releases the file and tells the operating system that all writes have been completed. The files do eventually get closed and there is a process in Python that cleans them up. The behaviour is unpredictable though. It is best practice to close them once done with however. f.close() ``` * The most common way is to close using the `with` statement. ``` with open('10_01_output.txt', 'a') as f: f.write('blah blah\n') f.write('other stuff\n') ``` * As soon as we out-dent the above code block, the above file is closed. * Running just `f.write('I forgot stuff')` also willl not work. You have to run the `close()` function.

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