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  • Finding a Eulerian Tour

    - by user590903
    I am trying to solve a problem on Udacity described as follows: # Find Eulerian Tour # # Write a function that takes in a graph # represented as a list of tuples # and return a list of nodes that # you would follow on an Eulerian Tour # # For example, if the input graph was # [(1, 2), (2, 3), (3, 1)] # A possible Eulerian tour would be [1, 2, 3, 1] I came up with the following solution, which, while not as elegant as some of the recursive algorithms, does seem to work within my test case. def find_eulerian_tour(graph): tour = [] start_vertex = graph[0][0] tour.append(start_vertex) while len(graph) > 0: current_vertex = tour[len(tour) - 1] for edge in graph: if current_vertex in edge: if edge[0] == current_vertex: current_vertex = edge[1] else: current_vertex = edge[0] graph.remove(edge) tour.append(current_vertex) break return tour graph = [(1, 2), (2, 3), (3, 1)] print find_eulerian_tour(graph) >> [1, 2, 3, 1] However, when submitting this, I get rejected by the grader. I am doing something wrong? I can't see any errors.

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  • List filtering: list comprehension vs. lambda + filter

    - by Agos
    I happened to find myself having a basic filtering need: I have a list and I have to filter it by an attribute of the items. My code looked like this: list = [i for i in list if i.attribute == value] But then i thought, wouldn't it be better to write it like this? filter(lambda x: x.attribute == value, list) It's more readable, and if needed for performance the lambda could be taken out to gain something. Question is: are there any caveats in using the second way? Any performance difference? Am I missing the Pythonic Way™ entirely and should do it in yet another way (such as using itemgetter instead of the lambda)? Thanks in advance

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  • Problems with 'while' loop and 'for' loop when reading through file

    - by David Beckham
    I wasted plenty of hours trying to figure out the problem but no luck. Tried asking the TA at my school, but he was useless. I am a beginner and I know there are a lot of mistakes in it, so it would be great if I can get some detail explanation as well. Anyways, basically what I am trying to do with the following function is: Use while loop to check and see if random_string is in TEXT, if not return NoneType if yes, then use a for loop to read lines from that TEXT and put it in list, l1. then, write an if statement to see if random_string is in l1. if it is, then do some calculations. else read the next line Finally, return the calculations as a whole. TEXT = open('randomfile.txt') def random (TEXT, random_string): while random_string in TEXT: for lines in TEXT: l1=TEXT.readline().rsplit() if random_string in l1: ''' do some calculations ''' else: TEXT.readline() #read next line??? return #calculations return None

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  • How do I attach event bindings to items on a canvas using Tkinter?

    - by Ian
    If I'm using a canvas to display data and I want the user to be able to click on various items on the canvas in order to get more information or interact with it in some way, whats the best way of going about this? Searching online I can find information about how to bind events to tags but that seems to be more indirect then what I want. I don't want to group items with tags, but rather have specific function calls when the user clicks specific items on the canvas.

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  • Yet another list comprehension question

    - by relima
    I had this: if Setting["Language"] == "en": f.m_radioBox3.SetSelection(0) elif Setting["Language"] == "pt": f.m_radioBox3.SetSelection(1) elif Setting["Language"] == "fr": f.m_radioBox3.SetSelection(2) elif Setting["Language"] == "es": f.m_radioBox3.SetSelection(3) Then I did this: Linguas = ["en","pt","fr","es"] a = 0 for i in Linguas: if i == Setting["Language"]: f.m_radioBox3.SetSelection(a) a += 1 Is it possible to further simplify this and make it into a one-liner?

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  • Decorator that can take both init args and call args?

    - by digitala
    Is it possible to create a decorator which can be __init__'d with a set of arguments, then later have methods called with other arguments? For instance: from foo import MyDecorator bar = MyDecorator(debug=True) @bar.myfunc(a=100) def spam(): pass @bar.myotherfunc(x=False) def eggs(): pass If this is possible, can you provide a working example?

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  • Object for storing strings geted from prints

    - by evg
    class MyWriter: def __init__(self, stdout): self.stdout = stdout self.dumps = [] def write(self, text): self.stdout.write(smart_unicode(text).encode('cp1251')) self.dumps.append(text) def close(self): self.stdout.close() writer = MyWriter(sys.stdout) save = sys.stdout sys.stdout = writer I use self.dumps list to store geted data from prints. Is it exists more convinient object for storing string lines in memory? ideally i want dump it to one big string. I can get it like this "\n".join(self.dumps) from code above. Mb it's better to just concat strings - self.dumps += text ?

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  • Using adaptive step sizes with scipy.integrate.ode

    - by Mike
    The (brief) documentation for scipy.integrate.ode says that two methods (dopri5 and dop853) have stepsize control and dense output. Looking at the examples and the code itself, I can only see a very simple way to get output from an integrator. Namely, it looks like you just step the integrator forward by some fixed dt, get the function value(s) at that time, and repeat. My problem has pretty variable timescales, so I'd like to just get the values at whatever time steps it needs to evaluate to achieve the required tolerances. That is, early on, things are changing slowly, so the output time steps can be big. But as things get interesting, the output time steps have to be smaller. I don't actually want dense output at equal intervals, I just want the time steps the adaptive function uses.

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  • Updating a module level shared dictionary

    - by Vishal
    Hi, A module level dictionary 'd' and is accessed by different threads/requests in a django web application. I need to update 'd' every minute with a new data and the process takes about 5 seconds. What could be best solution where I want the users to get either the old value or the new value of d and nothing in between. I can think of a solution where a temp dictionary is constructed with a new data and assigned to 'd' but not sure how this works! Appreciate your ideas. Thanks

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  • Django Find Out if User is Authenticated in Custom Tag

    - by greggory.hz
    I'm trying to create a custom tag. Inside this custom tag, I want to be able to have some logic that checks if the user is logged in, and then have the tag rendered accordingly. This is what I have: def user_actions(context): request = template.Variable('request').resolve(context) return { 'auth': request['user'].is_athenticated() } register.inclusion_tag('layout_elements/user_actions.html', takes_context=True)(user_actions) When I run this, I get this error: Caught VariableDoesNotExist while rendering: Failed lookup for key [request] in u'[{}]' The view that renders this ends like this: return render_to_response('start/home.html', {}, context_instance=RequestContext(request)) Why doesn't the tag get a RequestContext object instead of the Context object? How can I get the tag to receive the RequestContext instead of the Context? EDIT: Whether or not it's possible to get a RequestContext inside a custom tag, I'd still be interested to know the "correct" or best way to determine a user's authentication state from within the custom tag. If that's not possible, then perhaps that kind of logic belongs elsewhere? Where?

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  • Stopping long-running requests in Pylons

    - by Jack
    I'm working on an application using Pylons and I was wondering if there was a way to make sure it doesn't spend way too much time handling one request. That is, I would like to find a way to put a timer on each request such that when too much time elapses, the request just stops (and possibly returns some kind of error). The application is supposed to allow users to run some complex calculations but I would like to make sure that if a calculation starts taking too much time, we stop it to allow other calculations to take place.

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  • Indexing one-dimensional numpy.array as matrix

    - by Alain
    I am trying to index a numpy.array with varying dimensions during runtime. To retrieve e.g. the first row of a n*m array a, you can simply do a[0,:] However, in case a happens to be a 1xn vector, this code above returns an index error: IndexError: too many indices As the code needs to be executed as efficiently as possible I don't want to introduce an if statement. Does anybody have a convenient solution that ideally doesn't involve changing any data structure types?

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  • How to detect a sign change for elements in a numpy array

    - by cb160
    I have a numpy array with positive and negative values in. a = array([1,1,-1,-2,-3,4,5]) I want to create another array which contains a value at each index where a sign change occurs (For example, if the current element is positive and the previous element is negative and vice versa). For the array above, I would expect to get the following result array([0,0,1,0,0,1,0]) Alternatively, a list of the positions in the array where the sign changes occur or list of booleans instead of 0's and 1's is fine.

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  • index error:list out of range

    - by kaushik
    from string import Template from string import Formatter import pickle f=open("C:/begpython/text2.txt",'r') p='C:/begpython/text2.txt' f1=open("C:/begpython/text3.txt",'w') m=[] i=0 k='a' while k is not '': k=f.readline() mi=k.split(' ') m=m+[mi] i=i+1 print m[1] f1.write(str(m[3])) f1.write(str(m[4])) x=[] j=0 while j<i: k=j-1 l=j+1 if j==0 or j==i: j=j+1 else: xj=[] xj=xj+[j] xj=xj+[m[j][2]] xj=xj+[m[k][2]] xj=xj+[m[l][2]] xj=xj+[p] x=x+[xj] j=j+1 f1.write(','.join(x)) f.close() f1.close() It say line 33,xj=xj+m[l][2] has index error,list out of range please help thanks in advance

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  • does webapp has 'elseif' or 'elif' in template tags..

    - by zjm1126
    my code is : Hello!~~~ {% if user %} <p>Logged in as {{ user.first_name }} {{ user.last_name }}.</p> {% elif openid_user%} <p>Hello, {{openid_user.nickname}}! Do you want to <a href="{{openid_logout_url}}">Log out?</p> {% else %} <p><a href="/login?redirect={{ current_url }}">google Log in</a>.</p> <p><a href="/twitter">twitter Log in</a>.</p> <p><a href="/facebook">facebook Log in</a>.</p> <p><a href="{{openid_login_url}}">openid Log in</a>.</p> <iframe src="/_openid/login?continue=/"></iframe> {% endif %} the error is : TemplateSyntaxError: Invalid block tag: 'elif' does not webapp has a 'else if ' ? thanks

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  • How to access the calling source line from interactive shell

    - by TJD
    I want to make a function that can determine the source code of how it was called. I'm aware of how to do this generally with the inspect module. For example, this question, works well and provides my desired output in the lines variable as shown below: def hello(x): frame,filename,line_number,function_name,lines,index=\ inspect.getouterframes(inspect.currentframe())[1] print(frame,filename,line_number,function_name,lines,index) The problem is that this solution doesn't work in an interactive command line session. For example, from a command line, the result looks like: >>> y = hello(7) (<frame object at 0x01ECA9E8>, '<stdin>', 1, '<module>', None, None) The problem is that the source file is '<stdin>', so the lines variable is None. How can I access the calling line to find the result containing the string y = hello(7) during an interactive session?

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  • Google App Engine: Update model definitons?

    - by Rosarch
    I recently updated one of my models by adding a db.ListProperty(): class DependencyArcTail(db.Model): courses = db.ListProperty(db.Key) ''' newly added ''' forwardLinks = db.ListProperty(db.Key) However, I can't seem to get this to be reflected in the SDK dashboard. I cleared the datastore and reloaded it. Then I ran the procedures that create the DependencyArcTail objects. However, forwardLinks still doesn't show up as an attribute in the SDK dashboard. What's happening?

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  • Django & custom auth backend (web service) + no database. How to save stuff in session?

    - by Infinity
    I've been searching here and there, and based on this answer I've put together what you see below. It works, but I need to put some stuff in the user's session, right there inside authenticate. How would I store acme_token in the user's session, so that it will get cleared if they logged out? class AcmeUserBackend(object): # Create a User object if not already in the database? create_unknown_user = False def get_user(self, username): return AcmeUser(id=username) def authenticate(self, username=None, password=None): """ Check the username/password and return an AcmeUser. """ acme_token = ask_another_site_about_creds(username, password) if acme_token: return AcmeUser(id=username) return None ################## from django.contrib.auth.models import User class AcmeUser(User): objects = None # we cannot really use this w/o local DB def save(self): """saving to DB disabled""" pass def get_group_permissions(self): """If you don't make your own permissions module, the default also will use the DB. Throw it away""" return [] # likewise with the other permission defs def get_and_delete_messages(self): """Messages are stored in the DB. Darn!""" return []

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