diff -r 7206fe0c03c5 -r b595f90016c5 getting-started-files/script.rst --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/getting-started-files/script.rst Wed Oct 06 15:16:09 2010 +0530 @@ -0,0 +1,147 @@ +======== + Script +======== + +Welcome to the tutorial on getting started with files. + +{{{ Screen shows welcome slide }}} + +{{{ Show the outline for this tutorial }}} + +In this tutorial we shall learn to read files, and do some basic +actions on the file, like opening and reading a file, closing a +file, iterating through the file line-by-line, and appending the +lines of a file to a list. + +{{{ switch back to the terminal }}} + +As usual, we start IPython, using +:: + + ipython -pylab + +Let us first open the file, ``pendulum.txt`` present in +``/home/fossee/``. +:: + + f = open('/home/fossee/pendulum.txt') + +``f`` is called a file object. Let us type ``f`` on the terminal to +see what it is. +:: + + f + +The file object shows, the file which is open and the mode (read +or write) in which it is open. + +We shall first learn to read the whole file into a single +variable. Later, we shall look at reading it line-by-line. We use +the ``read`` method of ``f`` to read, all the contents of the file +into the variable ``pend``. +:: + + pend = f.read() + +Now, let us see what is in ``pend``, by typing +:: + + print pend + +We can see that ``pend`` has all the data of file. Type just ``pend`` +to see more explicitly, what it contains. +:: + + pend + +%%1%% Pause the video here and split the variable into a list, +``pend_list``, of the lines in the file and then resume the +video. Hint, use the tab command to see what methods the string +variable has. + +#[punch: should this even be put? add dependency to strings LO, +where we mention that strings have methods for manipulation. hint: +use splitlines()] +:: + + pend_list = pend.splitlines() + + pend_list + +Now, let us learn to read the file line-by-line. But, before that +we will have to close the file, since the file has already been +read till the end. +#[punch: should we mention file-pointer?] + +Let us close the file opened into f. +:: + + f.close() + +Let us again type ``f`` on the prompt to see what it shows. +:: + + f + +Notice, that it now says the file has been closed. It is a good +programming practice to close any file objects that we have +opened, after their job is done. + +Let us, now move on to reading files line-by-line. + +%%1%% Pause the video here and re-open the file ``pendulum.txt`` +with ``f`` as the file object, and then resume the video. + +We just use the up arrow until we reach the open command and issue +it again. +:: + + f = open('/home/fossee/pendulum.txt') + +Now, to read the file line-by-line, we iterate over the file +object line-by-line, using the ``for`` command. Let us iterate over +the file line-wise and print each of the lines. +:: + + for line in f: + print line + +As we already know, ``line`` is just a dummy variable, and not a +keyword. We could have used any other variable name, but ``line`` +seems meaningful enough. + +Instead of just printing the lines, let us append them to a list, +``line_list``. We first initialize an empty list, ``line_list``. +:: + + line_list = [ ] + +Let us then read the file line-by-line and then append each of the +lines, to the list. We could, as usual close the file using +``f.close`` and re-open it. But, this time, let's leave alone the +file object ``f`` and directly open the file within the for +statement. This will save us the trouble of closing the file, each +time we open it. + +for line in open('/home/fossee/pendulum.txt'): +line_list.append(line) + +Let us see what ``line_list`` contains. +:: + + line_list + +Notice that ``line_list`` is a list of the lines in the file, along +with the newline characters. If you noticed, ``pend_list`` did not +contain the newline characters, because the string ``pend`` was +split on the newline characters. + +{{{ show the summary slide }}} + +That brings us to the end of this tutorial. In this tutorial we +have learnt to open and close files, read the data in the files as +a whole, using the read command or reading it line by line by +iterating over the file object. + +Thank you! +