April 2019
Beginner
295 pages
5h 48m
English
Content preview from Think Julia
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Chapter 14. Files
This chapter introduces the idea of persistent programs that keep data in permanent storage, and shows how to use different kinds of permanent storage, like files and databases.
Persistence
Most of the programs we have seen so far are transient, in the sense that they run for a short time and produce some output, but when they end, their data disappears. If you run the program again, it starts with a clean slate.
Other programs are persistent: they run for a long time (or all the time); they keep at least some of their data in permanent storage (a hard drive, for example); and if they shut down and restart, they pick up where they left off.
Examples of persistent programs are operating systems, which run pretty much whenever a computer is on, and web servers, which run all the time, waiting for requests to come in on the network.
One of the simplest ways for programs to maintain their data is by reading and writing text files. We have already seen programs that read text files; in this chapter we will see programs that write them.
An alternative is to store the state of the program in a database. In this chapter I will also present how to use a simple database.
Reading and Writing
A text file is a sequence of characters stored on a permanent medium like a hard drive or flash memory. We saw how to open and read a file in “Reading Word Lists”.
To write a file, you have to open it with mode "w" as a second parameter:
julia>fout=open("output.txt","w")IOStream(<file ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.