[Tutor] Help needed with Python programming
My knowledge of coding is fairly limited and I am having a hard time writing a Python code which might be pretty simple for you :-) Here is what I am doing and I need help with: I have a python code that shows a set of shortest paths between nodes A and B. Now I have to select the least risky path among them. To do that I have to consider the risk values of each link. I know how to calculate the path's risk using its link value. For example: There is a path between node A and B wiht two links. Probability of failure for link 1 is 0.001 and for link 2 is 0.003. Here is the link with its risk values: A oo-o B 0.001 0.003 So the probability of the link being down will be: 1 - (0.999 x 0.997) = 0.996003 You can find the attached file with disaster risk values of each link. For instance; first line is : 1,3,5,0.03 -- this means, first disaster affects links 1-3 and 5-0 and its occurrence rate is 0.03. So you need to assign link (1-3)'s risk to 0.03. Then you will continue with the next disaster which is the one in the next line. Note that, if a link gets affected by 2 disasters, you will add the probability of those 2 disasters to find that link's risk. If anyone can help me code the first line, I will be able to do the rest. You need use array list and some functions like file reader and delimiter I guess. Thanks in advance. 1,3,5,0.03 2,3,5,5,4,0.11 3,3,5,5,4,5,8,0.04 2,5,8,7,8,0.04 3,14,10,14,13,17,13,0.04 1,14,18,0.06 4,10,13,14,13,17,13,12,13,0.04 4,11,6,11,9,11,12,11,19,0.08 3,19,20,15,20,21,20,0.24 1,21,20,0.05 3,20,21,21,16,21,22,0.27___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Help needed with Python programming
On 22/04/14 02:16, Suhana Vidyarthi wrote: I have a python code that shows a set of shortest paths between nodes A and B. It would help if you showed us this code. Otherwise we are just making wild guesses about how you are modelling this. Also knowing which Python version you are using would be good. If anyone can help me code the first line, I will be able to do the rest. You need use array list and some functions like file reader and delimiter I guess. Have you written these functions already? Are they part of some module or library you are using? Or is it the writing of these functions you want help with? Graph or network analysis is a fairly standard math problem. There are probably algorithms (or even solutions) in other languages (or even in Python if you are lucky) that you can convert if you do a search. -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ http://www.flickr.com/photos/alangauldphotos ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Help needed with Python programming
On Mon, Apr 21, 2014 at 06:16:20PM -0700, Suhana Vidyarthi wrote: [...] I have a python code that shows a set of shortest paths between nodes A and B. Now I have to select the least risky path among them. To do that I have to consider the risk values of each link. I know how to calculate the path's risk using its link value. For example: There is a path between node A and B wiht two links. Probability of failure for link 1 is 0.001 and for link 2 is 0.003. Here is the link with its risk values: A oo-o B 0.001 0.003 So the probability of the link being down will be: 1 - (0.999 x 0.997) = 0.996003 I don't think that calculation is correct. I think you mean that the probability of the link being UP is (0.999 x 0.997) = 0.996003, and the prob of it being DOWN is 1-0.996003 = 0.003997. So that path has a risk of 0.003997. You can find the attached file with disaster risk values of each link. For instance; first line is : 1,3,5,0.03 -- this means, first disaster affects links 1-3 and 5-0 and its occurrence rate is 0.03. So you need to assign link (1-3)'s risk to 0.03. Then you will continue with the next disaster which is the one in the next line. Note that, if a link gets affected by 2 disasters, you will add the probability of those 2 disasters to find that link's risk. If anyone can help me code the first line, I will be able to do the rest. You need use array list and some functions like file reader and delimiter I guess. Okay, let's start with reading the file. filename = path/to/file.txt Notice that I use forward slashes. Even if you are on Windows, you should code your paths with forward slashes. Either that, or you have to double every backslash: # on Windows either of these will be okay filename = C:/path/to/file.txt filename = C:\\path\\to\\file.txt Now let's read the file, one line at a time: filename = path/to/file.txt fp = open(filename, r) for line in fp: # process that single line ... How might we process the line? I'm not sure what your requirements are, but at a guess you'll want something like this: - ignore leading and trailing whitespace, including the end of line marker at the end of each line; - skip blank lines; - split non-blank lines into four fields; - convert the first three into integers; - and the last field into a float. filename = path/to/file.txt fp = open(filename, r) for line in fp: # process that single line line = line.strip() # ignore leading and trailing whitespace if not line: continue # skip blank lines a, b, c, d = line.split(,) # Split on commas a = int(a) # convert to an int instead of string b, c = int(b), int(c) d = float(d) # And now you can handle the values a, b, c, d ... And finally, when you are done, close the file: fp.close() Does this help? -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Help needed with Python programming
On 22/04/2014 12:41, Steven D'Aprano wrote: On Mon, Apr 21, 2014 at 06:16:20PM -0700, Suhana Vidyarthi wrote: [...] # on Windows either of these will be okay filename = C:/path/to/file.txt filename = C:\\path\\to\\file.txt Or a raw string r'C:\path\to\file.txt' -- My fellow Pythonistas, ask not what our language can do for you, ask what you can do for our language. Mark Lawrence --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Help needed with Python programming
Unfortunately, we can't give too much specific help on your particular problem because it's homework. You should use the knowledge you learned in your introductory programming class about designing programs. In particular, give a name to the function or functions your are designing. Be rigorous in the terms you are using when you talk about the problem. Formalize what the types of inputs and outputs are. Probably most importantly, express test cases that will demonstrate what you want the output to be. And not hand-wavy things, but actual test cases that you can execute. What's the expected result of parsing the first line? That is, you're saying that the string: 1,3,5,0.03 has some kind of meaning that can be parsed. Can you express this meaning as a data structure? Can you give that data structure a name? Can you write a unit test that can test that your parser is behaving properly? ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
