Mailman 3 May 2002 - Edu-sig

Python @ Education: What are your problems?
by Ingo Linkweiler 07 Jun '02

07 Jun '02

Hello, are you using python for teaching programing? I am just writing a diploma paper about python and want to know your experiences with python. What do you like when teaching python? For example: - Easy readable syntax - High Level language - Lists, Tupels, Dictionaries included - interpreter: Everything can be tested - Many tools available ..... AND MORE IMPORTANT: What are your problems with python? Are pupils/students having any problems or often asked questions? What do you dislike at python? For example: - When teaching C or Pascal, newbies do not know, where to set a ";" and where not. Any similar problems with Python? - Why must I set a ":" after "if" or "for" ? " if x == y : " ..... I hope you have many suggestions. regards, Ingo

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Sandboxing python programs
by Louis Bertrand 01 Jun '02

01 Jun '02

A while back I asked if there was any way of sandboxing a Python application beyond a chroot jail to run submitted programs in a batch and pre-grade them. Here's something that looks promising: http://www.citi.umich.edu/u/provos/systrace/ Ciao --Louis

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PyQwt - data plotting for Python
by Burley, Brent 01 Jun '02

01 Jun '02

I haven't tried this, but it looks really nice: http://gerard.vermeulen.free.fr I do use Qt and PyQt quite a bit and recommend both highly. Brent

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Re: Python @ Education: What are your problems?
by Burley, Brent 01 Jun '02

01 Jun '02

> From: Kirby Urner <urnerk(a)qwest.net> ... > def readln(): # defined once > return [eval(i) for i in raw_input().split()] > > x,y = readln() # used elsewhere > > is a quickie workaround. Clever, and concise! Here's a more robust (albeit verbose) version that checks the number and types of the arguments: def readln(spec, prompt=""): types = { 'i' : int, 'f' : float, 's' : str } while 1: words = raw_input(prompt).split() if len(words) != len(spec): print 'You must input', len(spec), 'items, please try again' continue try: return [types[s](w) for s,w in zip(spec, words)] except KeyError: print 'Invalid type specifier passed to readln:', s print " You must pass in a string of i's, f's, or s's" return except ValueError, e: print 'Invalid input, please try again' print ' ', e >>> print readln('ifs', 'input (int float string): ') input (int float string): You must input 3 items, please try again input (int float string): a b c Invalid input, please try again invalid literal for int(): a input (int float string): 1 2 3 [1, 2.0, '3'] >>> Or, if you only care about inputting numbers, you can use this simpler version: def readnumbers(num, prompt=""): while 1: words = raw_input(prompt).split() if len(words) != num: print 'You must input', num, 'numbers, please try again' continue try: return [float(w) for w in words] except ValueError, e: print 'Invalid input, please try again' print ' ', e >>> readnumbers(3, 'x y z? ') x y z? 1 2 You must input 3 numbers, please try again x y z? 1 2 z Invalid input, please try again invalid literal for float(): z x y z? 1 2 3 [1.0, 2.0, 3.0] Brent

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Re: [Edu-sig] Python @ Education: What are your problems?
by Louis Bertrand 01 Jun '02

01 Jun '02

[warning to edu-sig readers -- somewhat long] Hello, I use Python to teach the first year programming course in the "computer systems" and "computer programmer" streams in the School of Technology here at Durham College. The intent of this course is to take students with no prior programming experience and teach them the fundamentals: variables, branches, loops, functions, objects and a bit (excuse the term) of binary & hex. Students are from mixed backgrounds (fresh out of high school, returning to school as mature student, foreign students), aiming for practical, hands-on training as opposed to university-style courses. The experience has been mixed but mostly good. Java was the first choice for this course but I got nightmares at the thought of teaching monstrosities like: class HelloWorld { public static void main(String[] args) { System.out.println("Hello World"); } } instead of: print "Hello World" Interpreted rather than compiled: driving the interpreter directly, line by line is great for in-class demonstrations because I can "walk" through an example, then run it full speed from the .py file. This is especially good for Tkinter examples. Objects: Python's object model is simple and uncluttered so that's good. However the "self" reference in method parameter lists and for instance variables is a source of aggravation. There is trouble reconciling the fact that a method is nested in the class definition, but it still needs to be told about itself, and all instance variables need to also be referenced. Java's "this" is more subtle -- you don't see it, but it's there when you need it. You don't need to introduce it immediately. Dynamic typing: mixed blessing. Students don't trip on types, but they aren't prepared for the strict typing in Java and the little disasters due to type errors in C. Simpler syntax. No squiggles and semicolons to worry about. However, this leaves the students unprepared for the squiggles and semicolons in C, C++ and Java. Indenting block structure. Nice because it matches the pseudocode I do in class. However, some students often don't get it and occasionally give me: if x == y : # do some stuff else : # do something else # Sorry, I couldn't get it to work. It kept giving me errors :( Basically, since IDLE keeps suggesting an indent, they never de-indent when they are done the particular block. The fact that nobody around here had heard of Python before I started has been a constant aggravation. "If it's not popular, it can't be any good" (read between the lines: "if it didn't come from Microsoft, it's no good"), or the even deadlier slag "it won't help our grads get a job"). This leads to pushback from other teachers and some students who feel I'm teaching something totally irrelevant and "out in left field". Visual Basic, C, C++, Java and Turing are the alternatives proposed. (References and "ammunition" welcome). IDLE, while it meets its design goals for portability and simplicity, may be _too_ simple. For example, IDLE doesn't even let students print out their work -- I have to get them to copy and paste their console output to Notepad. I'm afraid that we have to "market" to students these days, and the glitz and flash of Microsoft Visual Studio totally obliterates IDLE. I need to find a more Microsoft-oriented IDE (but not python for dot N0T) . Anyway, that's it for now (I vented my frustrations). On the whole, I'll keep doing the course my way. I want to change a few things, but Python stays. If there are points you'd like me to follow up, feel free to ask privately or on the edu-sig list. Ciao --Louis Louis Bertrand Durham College, Oshawa, Canada louis.bertrand(a)durhamc.on.ca

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Emulating Pascal input
by Michael Williams 25 May '02

25 May '02

Hi, We're currently running a trial implementation of a teaching course in Python here at the University of Oxford Physics department. The current course uses Pascal and, although it works well, is obviously sub-optimal for a modern undergraduate education. Details of the results of the trial will be posted to EDU-sig when it is complete, but for now we're trying to address what we see as a limitation of Python for introductory programming, namely input. Consider the following Pascal code: (******** Pascal code **********) (* Pascal ascii input of numbers: stdin and file *) readln(x, y); readln(fin, x, y); The first line is for stdin, the second for from file. The variables x and y will then contain the first two white space separated numbers the program encounters when that function is called. Here's how we're currently getting students to do the equivalent in Python: ######### Python code ########### # Either: stdin linestring = raw_input() # Or: file linestring = f.readline() linelist = string.split(linestring) x = int(linelist[0]) y = int(linelist[1]) # Or perhaps linestring = raw_input() x,y = string.split(linestring) # x and y are now strings eg. '1' # and '2' x = int(x) y = int(y) Having read through the many threads on this topic on comp.lang.python I realise and understand that modern programs' input generally requires thought and customization from the program author. However, we strongly feel there should be an equivalent to Pascal's readln (which is basically C's scanf but without the formatting strings) for simple, generally numerical, whitespace-separated input. In the two weeks out trial has been running (one to go), students' attempts to read in simple two column tables from a file has consistently caused problems due to the (relative!) complexity of string splitting. However, There is no need for a scanf (if your input is sufficiently complex to require formatting strings then either string or regex splitting is definitely a more elegant solution). I have been attempting to write such a function in Python but have been struggling with (a) the lack of pointers, and (b) my total ignoarnce of classes, which I suspect would be helpful. Here's what I have so far (although note there is no error handling--give it a string response and it falls over and dies, give it the wrong number of responses and it falls over and dies, etc., etc.): ############ ninput.py ############ import string def ninput(n, fin = None, prompt = '', sep = None): # If not file input then get string from stdin, else get from file if fin == None: linestring = raw_input(prompt) else: linestring = fin.readline() # Split up into list with optional seperator argument responses = string.split(linestring, sep) for i in range(len(responses)): if '.' in responses[i] or 'e' in responses[i] or \ 'E' in responses[i]: # i.e. if it looks like a float responses[i] = float(responses[i]) else: # i.e if it doesn't look like a float responses[i] = int(responses[i]) # If there was only one response then don't return a list. if len(responses) == 1: responses = responses[0] return responses[:n] #################################### And here is a usage example: >>> x, y = ninput(2) 5 6.0 >>> print x, type(x) 5 <type 'int'> >>> print y, type(y) 6.0 <type 'float'> This has the limitation that the user must pass the number of results they expect back. This is done implicitly in the Pascal version too (the number of variables passed to the function). However, error checking is difficult as this version stands. If the student using the ninput function does, e.g. >>> x = ninput(2) 5 6.0 [5, 6.0] <type 'list'> This is possibly what should be expected. However, passing the numerical argument representing the number of results expected does not strike me as a particularly graceful solution. We would prefer something like the Pascal way, where the global variables in which the results are to be stored are passed as parameters. Can anyone suggest a way of doing this? And if such an equivalent to the Pascal construct was implemented, what would be the chances of getting it included in, say, the string module of core Python. We would like such a function but would be reluctant to use it as we would then be teaching our students a ``dialect'' of Python. -- Michael Williams

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by lolita 24 May '02

24 May '02

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Re: Emulating Pascal input
by Siemssen, Bradford 22 May '02

22 May '02

Michael, I'd recommend using the input function as suggested by Guido. However, if you really feel the need to get the functionality you described try this. I modified your original routine to have more error handling, and to be a bit more robust. Note I haven't tested this myself, I'm writing this on company time, and hey it's python it often works first try, but look over the code and you should get an idea how to make it work. The code below when given non-number values in the input will interpret the values as some default value (typically zeros). The code will prompt the user to re-enter the values when used interactively when the "strictInput" flag is passed to the function. Note "strictInput" is incompatible with reading from a file, there is no way to prompt a file to re-enter bad input. When the conflict is found an exception is thrown. The code could be simplified by removing the strictInput flag and associated logic entirely. Cheers, Brad The new code is below. ############ ninput.py ############ import string # You will need the input part as a separate function so you can use it # easily when dealing with errors. def promptedSeparatedInput(fin, prompt, sep): # If not file input then get string from stdin, else get from file if fin == None: linestring = raw_input(prompt) else: linestring = fin.readline() # Split up into list with optional seperator argument responses = string.split(linestring, sep) return responses def ninput(n, fin = None, prompt = '', sep = None, strictInput = 0, errMsg = "Enter numbers numbskull!!", defaultValue = 0.0): if strictInput and fin != None: raise "invalid parameters to ninput, can not use strictInput with a file" # force reading the input at least once, technically since we don't have # any input yet there is an error that will be remedied by getting it. inputErrors = 1 while inputErrors: # Assume everything will go right, and we don't have to # continue this loop. Error handling code may change that though. inputErrors = 0 # Get the input. responses = promptedSeparatedInput(fin, prompt, sep) for i in range(len(responses)): # You need to catch exceptions that may occur # when converting data of the wrong type try: if '.' in responses[i] or 'e' in responses[i] or \ 'E' in responses[i]: # i.e. if it looks like a float responses[i] = float(responses[i]) else: # i.e if it doesn't look like a float responses[i] = int(responses[i]) except: # when doing strict input checking, print the error message, # and keep the while loop from terminating so we will get the # input from the user again. if strictInput: inputErrors = 1 print errMsg break # exit the for loop else: # When not doing strictInput just set the value to the default. responses[i]= defaultValue # you should take care of the case where less was entered than was # expected, fill in spaces with the default value. while (n - len(responses)) > 0: responses.append(defaultValue) # If there was only one response then don't return a list. #wrong -> if len(responses) == 1: responses = responses[0] # you really mean if only one response was _EXPECTED_ then don't return a list if n == 1: return responses[0] return responses[:n] ############## example usage: x = ninput(2) x [5, 6.0] # use list unpacking instead of unpacking the list by hand, # note you'll get an exception if the number of variables to # unpack into is different than the number returned. x, y, z = ninput(3) # or just assign the resulting list x = ninput(3) P.S. Regarding passing the values you want the results stored in to the function is not possible using python. All variables are just references, and parameters are local variables, so they are copies of references. Changing what a local variable references does not change what the outer variable references.

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Re: [Edu-sig] Converting from Qbasic
by Nicholas Wheeler 13 May '02

13 May '02

Thank you very much, it turns out, i emailed the creator of ioport, and he updated it immediatly. This looks like the exact thing i have been looking for. Nick _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp.

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RE: [Edu-sig] Converting from Qbasic
by Nicholas Wheeler 13 May '02

13 May '02

Hello, i am one of the students that started this thread. I found the first email, directing me to winioport to be the most helpful. I did a quick search for a newer version of calldll (python2.2), and found it. I have gotten my program to work on windows 2000, and windows 95. Unfortuantly, Winioport only works on windows . . . I was wondering if anybody knew of a program which would send byte data out to the parallel port in linux. This would be very helpfull. --Nick _________________________________________________________________ Send and receive Hotmail on your mobile device: http://mobile.msn.com

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