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  • How to remove certain lists from a list of lists using python?

    - by seaworthy
    I can not figure out why my code does not filter out lists from a predefined list. I am trying to remove specific list using the following code. data = [[1,1,1],[1,1,2],[1,2,1],[1,2,2],[2,1,1],[2,1,2],[2,2,1],[2,2,2]] data = [x for x in data if x[0] != 1 and x[1] != 1] print data My result: data = [[2, 2, 1], [2, 2, 2]] Expected result: data = [[1,2,1],[1,2,2],[2,1,1],[2,1,2],[2,2,1],[2,2,2]]

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  • I'm making a resume...what would you consider as intermediate python programming skills?

    - by user285884
    I've made a couple of scripts. One is a stock screener that can search through every stock. Another creates a heatmap that tells you what's performed well and badly over the past day. They aren't really that useful, just did them to work on my programming skills. I was able to throw some SQL in my scripts too. Would you call that intermediate? Thanks? How do you guys list your programming skills on your resume? Maybe there's a better way of putting it on my resume than "intermediate" or "beginner."

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  • How to select random image of specific size using Django / Python?

    - by Jonathan
    I've been using this little snippet to select random images. However I would like to change it to select only images of a certain size. I'm running into trouble checking against image size. If I use get_image_dimensions() I need to use a conditional statement, which then requires that I allow exceptions. So, I guess I need some pointers on just limiting by image dimensions. Thanks. import os import random import posixpath from django import template from django.conf import settings register = template.Library() def is_image_file(filename): """Does `filename` appear to be an image file?""" img_types = [".jpg", ".jpeg", ".png", ".gif"] ext = os.path.splitext(filename)[1] return ext in img_types @register.simple_tag def random_image(path): """ Select a random image file from the provided directory and return its href. `path` should be relative to MEDIA_ROOT. Usage: <img src='{% random_image "images/whatever/" %}'> """ fullpath = os.path.join(settings.MEDIA_ROOT, path) filenames = [f for f in os.listdir(fullpath) if is_image_file(f)] pick = random.choice(filenames) return posixpath.join(settings.MEDIA_URL, path, pick)

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  • The return value should be a list but doesn't return as expected?! - Python newbie

    - by user1432941
    Hi this must be a very simple solution that has eluded me this last hour. I've tried to build this test function where the return value of the test_cases list should match the values in the test_case_answers list but for some reason, test case 1 and test case 2 fail. When i print the return values for the test cases they return the correct answers, but for some reason test case 1 and test case 2 return False. Thanks for your help! import math test_cases = [1, 9, -3] test_case_answers = [1, 3, 0] def custom_sqrt(num): for i in range(len(test_cases)): if test_cases[i] >= 0: return math.sqrt(test_cases[i]) else: return 0 for i in range(len(test_cases)): if custom_sqrt(test_cases[i]) != test_case_answers[i]: print "Test Case #", i, "failed!" custom_sqrt(test_cases)

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  • Python raises a KeyError (for an out of dictionary key) even though the key IS in the dictionary

    - by ignorantslut
    I'm getting a KeyError for an out of dictionary key, even though I know the key IS in fact in the dictionary. Any ideas as to what might be causing this? print G.keys() returns the following: ['24', '25', '20', '21', '22', '23', '1', '3', '2', '5', '4', '7', '6', '9', '8', '11', '10', '13', '12', '15', '14', '17', '16', '19', '18'] but when I try to access a value in the dictionary on the next line of code... for w in G[v]: #note that in this example, v = 17 I get the following error message: KeyError: 17 Any help, tips, or advice are all appreciated. Thanks.

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  • lambda vs. operator.attrgetter('xxx') as sort key function in Python

    - by Paul McGuire
    I am looking at some code that has a lot of sort calls using comparison functions, and it seems like it should be using key functions. If you were to change seq.sort(lambda x,y: cmp(x.xxx, y.xxx)), which is preferable: seq.sort(key=operator.attrgetter('xxx')) or: seq.sort(key=lambda a:a.xxx) I would also be interested in comments on the merits of making changes to existing code that works.

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  • Python - Is a dictionary slow to find frequency of each character?

    - by psihodelia
    I am trying to find a frequency of each symbol in any given text using an algorithm of O(n) complexity. My algorithm looks like: s = len(text) P = 1.0/s freqs = {} for char in text: try: freqs[char]+=P except: freqs[char]=P but I doubt that this dictionary-method is fast enough, because it depends on the underlying implementation of the dictionary methods. Is this the fastest method?

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  • Are python list comprehensions always a good programming practice?

    - by dln385
    To make the question clear, I'll use a specific example. I have a list of college courses, and each course has a few fields (all of which are strings). The user gives me a string of search terms, and I return a list of courses that match all of the search terms. This can be done in a single list comprehension or a few nested for loops. Here's the implementation. First, the Course class: class Course: def __init__(self, date, title, instructor, ID, description, instructorDescription, *args): self.date = date self.title = title self.instructor = instructor self.ID = ID self.description = description self.instructorDescription = instructorDescription self.misc = args Every field is a string, except misc, which is a list of strings. Here's the search as a single list comprehension. courses is the list of courses, and query is the string of search terms, for example "history project". def searchCourses(courses, query): terms = query.lower().strip().split() return tuple(course for course in courses if all( term in course.date.lower() or term in course.title.lower() or term in course.instructor.lower() or term in course.ID.lower() or term in course.description.lower() or term in course.instructorDescription.lower() or any(term in item.lower() for item in course.misc) for term in terms)) You'll notice that a complex list comprehension is difficult to read. I implemented the same logic as nested for loops, and created this alternative: def searchCourses2(courses, query): terms = query.lower().strip().split() results = [] for course in courses: for term in terms: if (term in course.date.lower() or term in course.title.lower() or term in course.instructor.lower() or term in course.ID.lower() or term in course.description.lower() or term in course.instructorDescription.lower()): break for item in course.misc: if term in item.lower(): break else: continue break else: continue results.append(course) return tuple(results) That logic can be hard to follow too. I have verified that both methods return the correct results. Both methods are nearly equivalent in speed, except in some cases. I ran some tests with timeit, and found that the former is three times faster when the user searches for multiple uncommon terms, while the latter is three times faster when the user searches for multiple common terms. Still, this is not a big enough difference to make me worry. So my question is this: which is better? Are list comprehensions always the way to go, or should complicated statements be handled with nested for loops? Or is there a better solution altogether?

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  • Is there a way to change lookandfeel for wx Python?

    - by uberjumper
    Hi, i was curious if there is some sort of way to change the look and feel of wxpython to something that is more standardized. I am writing a small application for windows and mac os x. And i noticed that Mac formats the layout and look of my application pretty terribly. I looked around online and could not find anything. Any ideas?

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  • Python: What's a correct and good way to implement __hash__()?

    - by random-name
    What's a correct and good way to implement hash()? I am talking about the function that returns a hashcode that is then used to insert objects into hashtables aka dictionaries. As hash() returns an integer and is used for "binning" objects into hashtables I assume that the values of the returned integer should be uniformly distributed for common data (to minimize collisions). What's a good practice to get such values? Are collisions a problem? In my case I have a small class which acts as a container class holding some ints, some floats and a string.

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  • What is the difference between "a is b" and "id(a) == id(b)" in Python?

    - by bp
    The id() inbuilt function gives... an integer (or long integer) which is guaranteed to be unique and constant for this object during its lifetime. The is operator, instead, gives... object identity So why is it possible to have two objects that have the same id but return False to an is check? Here is an example: >>> class Test(): ... def test(): ... pass >>> a = Test() >>> b = Test() >>> id(a.test) == id(b.test) True >>> a.test is b.test False A more troubling example: (continuing the above) >>> b = a >>> b is a True >>> b.test is a.test False >>> a.test is a.test False

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  • Extracting data from a text file to use in a python script?

    - by Rob
    Basically, I have a file like this: Url/Host: www.example.com Login: user Password: password How can I use RegEx to separate the details to place them into variables? Sorry if this is a terrible question, I can just never grasp RegEx. So another question would be, can you provide the RegEx, but kind of explain what each part of it is for?

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  • Building up an array in numpy/scipy by iteration in Python?

    - by user248237
    Often, I am building an array by iterating through some data, e.g.: my_array = [] for n in range(1000): # do operation, get value my_array.append(value) # cast to array my_array = array(my_array) I find that I have to first build a list and then cast it (using "array") to an array. Is there a way around these? all these casting calls clutter the code... how can I iteratively build up "my_array", with it being an array from the start? thanks.

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  • Python - 2 Questions: Editing a variable in a function and changing the order of if else statements

    - by Eric
    First of all, I should explain what I'm trying to do first. I'm creating a dungeon crawler-like game, and I'm trying to program the movement of computer characters/monsters in the map. The map is basically a Cartesian coordinate grid. The locations of characters are represented by tuples of the x and y values, (x,y). The game works by turns, and in a turn a character can only move up, down, left or right 1 space. I'm creating a very simple movement system where the character will simply make decisions to move on a turn by turn basis. Essentially a 'forgetful' movement system. A basic flow chart of what I'm intending to do: Find direction towards destination Make a priority list of movements to be done using the direction eg.('r','u','d','l') means it would try to move right first, then up, then down, then left. Try each of the possibilities following the priority order. If the first movement fails (blocked by obstacle etc.), then it would successively try the movements until the first one that is successful, then it would stop. At step 3, the way I'm trying to do it is like this: def move(direction,location): try: -snip- # Tries to move, raises the exception Movementerror if cannot move in the direction return 1 # Indicates movement successful except Movementerror: return 0 # Indicates movement unsuccessful (thus character has not moved yet) prioritylist = ('r','u','d','l') if move('r',location): pass elif move('u',location): pass elif move('d',location): pass elif move('l',location): pass else: pass In the if/else block, the program would try the first movement on the priority on the priority list. At the move function, the character would try to move. If the character is not blocked and does move, it returns 1, leading to the pass where it would stop. If the character is blocked, it returns 0, then it tries the next movement. However, this results in 2 problems: How do I edit a variable passed into a function inside the function itself, while returning if the edit is successful? I have been told that you can't edit a variable inside a function as it won't really change the value of the variable, it just makes the variable inside the function refer to something else while the original variable remain unchanged. So, the solution is to return the value and then assign the variable to the returned value. However, I want it to return another value indicating if this edit is successful, so I want to edit this variable inside the function itself. How do I do so? How do I change the order of the if/else statements to follow the order of the priority list? It needs to be able to change during runtime as the priority list can change resulting in a different order of movement to try.

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  • How do I send this email in Python, opening files and stuff?

    - by alex
    msg = EmailMessage(subject, body, from_email, [to_email]) msg.content_subtype = "html" msg.send() This is how I send an email in Django. But what if I want to open a text file and take into account all its line breaks and tabs. I want to take the body of the text file (with line breaks \n) and email it as text of the "body".

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