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This way, you can remove some crypticness, AND have all of the items from a certain module.

Conclusion

That's it! A very simple lesson, but now you can organise your programs very neatly. In fact, now it is increadibly easy to make progams that can grow in complexity without ending up with one cryptic file that is full of bugs.

Modules are great for importing code. Next lesson, we learn about file input and output, and the saving of information inside classes, to be retrieved later. Will be great! But until then...

Thanks to all,

sthurlow.com

File I/O

Introduction

Last lesson we learnt how to load external code into our program. Without any introduction (like what I usually have), let's delve into file input and output with normal text files, and later the saving and restoring of instances of classes. (Wow, our lingo power has improved greatly!)

Opening a file

To open a text file you use, well, the open() function. Seems sensible. You pass certain parameters to open() to tell it in which way the file should be opened - 'r' for read only, 'w' for writing only (if there is an old file, it will be written over), 'a' for appending (adding things on to the end of the file) and 'r+' for both reading and writing. But less talk, lets open a file for reading (you can do this in your python idle mode). Open a normal text file. We will then print out what we read inside the file:

Code Example 1 - Opening a file

openfile = open('pathtofile', 'r')

openfile.read()

That was interesting. You'll notice a lot of '

' symbols. These represent newlines (where you pressed enter to start a new line). The text is completely unformatted, but if you were to pass the output of openfile.read() to print (by typing print openfile.read()) it would be nicely formatted.

Seek and You Shall Find

Did you try typing in print openfile.read()? Did it fail? It likely did, and reason is because the 'cursor' has changed it's place. Cursor? What cursor? Well, a cursor that you really cannot see, but still a cursor. This invisible cursor tells the read function (and many other I/O functions) where to start from. To set where the cursor is, you use the seek() function. It is used in the form seek(offset, whence).

whence is optional, and determines where to seek from. If whence is 0, the bytes/letters are counted from the beginning. If it is 1, the bytes are counted from the current cursor position. If it is 2, then the bytes are counted from the end of the file. If nothing is put there, 0 is assumed.

offset decribes how far from whence that the cursor moves. for example:

* openfile.seek(45,0) would move the cursor to 45 bytes/letters after the beginning of the file.

* openfile.seek(10,1) would move the cursor to 10 bytes/letters after the current cursor position.

* openfile.seek(-77,2) would move the cursor to 77 bytes/letters before the end of the file (notice the - before the 77)

Try it out now. Use openfile.seek() to go to any spot in the file and then try typing print openfile.read(). It will print from the spot you seeked to. But realise that openfile.read() moves the cursor to the end of the file - you will have to seek again.

Other I/O Functions

There are many other functions that help you with dealing with files. They have many uses that empower you to do more, and make the things you can do easier. Let's have a look at tell(), readline(), readlines(), write() and close().