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In this self-check exercise,
I'd like you to try

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the update process that I presented to you

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in the preceding video.

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This time, looking specifically for

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the last name Doe and
updating it to Smith.

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Now if by any chance you're switching from

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IPython into Jupiter
to do the lab exercise

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I just want to point out
that the Jupiter files

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are in a separate folder from where

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I've been demonstrating IPython.

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So for example I had to
copy my accounts.txt file

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into the snippets_ipynb folder

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in order to demonstrate the
solution to this exercise.

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So go ahead and try the
exercise on your own,

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then come back to see the answer.

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Okay, let's go ahead and take a look.

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As you can see we're first going to open

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the accounts.txt file for reading.

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And we are going to open a
temporary file for writing.

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And again we're going to
write all of the content

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before the record that needs updating

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into the temporary file,
then we're going to

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write the updated record
into the temporary file.

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Then we're going to write the rest

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of the original accounts.txt
file into the temporary file,

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and then finally we're going
to delete the original file

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and rename the temporary file as well.

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So first let's do the writing process

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for which we have the with
statement you see here.

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And again accounts and temp file

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will automatically be closed when

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the with statement terminates.

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For every record in the accounts file

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we're going to split apart the record

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into it's three pieces of information,

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looking specifically for the
record that contains Doe.

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If the name does not contain Doe,

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then we will simply write
the original record out.

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Otherwise we will create our new record

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by joining together, separated by spaces,

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the list of arguments consisting of

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account, Smith, and balance.

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And again notice that that's
in square brackets there

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because the join method expects

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to receive as an argument
a sequence object.

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So that'll create the new record,

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then we'll write it out to disk,

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If it was not the record
that needed updating

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we'll keep writing out the other records

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until the file accounts has been

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fully read into memory.

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So let's go ahead and execute that.

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Now we have our temporary file set up,

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and so the next thing we're going to do

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is use the operating system module OS

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to enable us to remove
the original record,

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I'm sorry original file, accounts.txt

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so now that no longer exists.

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Then we're going to
rename the original file.

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And finally, so that we can check that

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the original file does
exist and has been updated,

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we're going to list out its contents

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using a command line command.

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Now for those of you on Mac OS and lenox

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you can use this first command cat,

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otherwise you can use more on Windows.

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And you can see that indeed
we have the updated record.

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And now instead of Doe for record 200

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we have the name Smith.

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And you can go back and confirm previously

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that we had the name Doe in that record.