You're watching the Python Coder. In this video we look at how to read a file.
Do you take out all your money when you go shopping? No. When you were eating
snacks and you and you want to eat some do you take all of them out? No. In a file
everything is a string so you could take out all the string or you could just
take it out by one end. So your choices read everything or get a piece by piece.
Well how do you do that? When you read a file you put it all in memory you can
use a file handle to take out parts of the file bit by bit.
What is a file handle? Well this is an object that points at the file a bit
like this arrow here and it can go down the file and retrieve bit by bit so when
we want to get data we can get for example line by line. So in a file
you see many different lines in this example represented by the different
lines of string but your computer doesn't see that your computer sees a
continuous string so how does it know what lines to produce? Well that's a
newline character this \n and that means each line that you see has
this newline character at the end so we have a continuous string but with these
newline characters telling the computer when a newline occurs.
Let's have a look at an example. Here's a file with people's names and their
scores now this is a continuous string we have the name a space a score which
is an integer and then the newline character so that's all one string to
the computer. So remember when we get data we get each line, each line and the
name and the score and the newline character. We don't want the newline
character so we can use strip. So here we've got the data without the newline
character. Everything is a string so if you want to do anything with the numbers
as an integer then you need to change them to either an integer or to a float.
So you're converting the type. So first of all each line we're going to split so
we split it into x and y the X being the name and Y being the score and we want
to change the score from being a string to an integer so here we just use int Y.
How about writing to a file? It's the same in a sense that we have this file
handle and we've got for example that people's names and their scores we want
to write them into a file. Remember we need to make everything a string so if
we've got numbers they need to change, well you need to change their type to a
string. So again in our example we've got the name and a scores and we need to
change those integers to strings. So what do we do when we write? We open the file,
we write the name, we write the score which we change to a string and then
we're going to close the file so that means the new folder we've created has
the people's names and their scores inside. So that makes our new file with
the scores in.
Let's look at some code including our example here we're going to read
everything so we've got our file called test it's a text document we're going to
open it we don't have to use the R but the R stands for read so we've got open
an our file name and a flag for read or write for example and then we're just
gonna print what the file handle is dot read so that reads everything into
a file using a file handle. So here we've got the same code but instead of reading
everything we're going to use a for loop with the line using a file handle and
then print each line. In our example we had to strip each line of the newline
character so here we see line equals line dot strip, then in our example we
spent the names and the scores here we've got x and y equals line dot split.
We had to change the string scores into numbers into ints so we've got int(y)
and finally we put our names and scores inside a scores dictionary so here's the
full code for that. There is an alternative method of opening files and
that's using 'with'. So here we have the same code except 'with' open file as file
and then we've got our for loop. We can do the same we've read as well using with
The advantage of 'with' is that you can close the file so people tend to like
that it automatically closes a file after opening it. Remember if you're
going to use file handling then the file should be in the same folder as your
program. If it's not then there are ways that you can access
which folder or directory you want where the file is but for now we're going to
assume that file is in the same folder as your Python file. What about writing
to a file? Similar code but here we've got this handle out and we've got open
the file and the W standing for write. We have a for loop so here we're going
to go through all the names and scores in the scores' dictionary and we're
going to write the name which is a string the score which we're going to
change to a string so string of Y plus the newline character remember we can use
the plus symbol to concatenate strings and then in this example we're going to
close the file so out.close. If you prefer use with here's the code very
similar we don't need to close it after because we're using the with method.
One thing to notice we've got my file dot txt if it already exists we're going to
write over it so be careful if you're going to use a file name then
you're going to delete that file if it already exists in that folder so be
careful there .We're going to finish with some terms file handle an object that
can access a file slash n stands for newline and that's used to split a
continuous string into lines of text such as in a file. Strip is the function
we use to remove unwanted characters like the newline character and also
unwanted spaces, read we're going to put all the text file into memory, finally
write is a function when we want to put text into a file. OK I hope you enjoyed
it if you did please click the like and if you haven't already please subscribe
thank you for watching and see you for the next video.
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