I have code that gets information from iTunes based on a search term that returns a list of dictionaries with various media types in it. I would like to group this information by whether or not it is a movie, song, or other media type. I want to do this within a function for later use, and was thinking the best way to do this would be to append each dictionary to a list based on what type it is. I am getting empty lists, even though the input I am putting in the function is a list of 100 dictionaries. Is there a better way to do this? This is my code -
def make_object(list_from_req):
movie_lst = []
song_lst = []
media_other_lst = []
for d in list_from_req:
if d['kind'] == 'song':
song_lst.append
elif d['kind'] == 'feature-movie':
movie_lst.append
else:
media_other_lst.append
return movie_lst, song_lst, media_other_lst
movie_lst.append by itself doesn’t do anything: it refers to the idea of adding to that particular list (which is sometimes very useful!) but it doesn’t use it. You have to pass arguments with () to call a function (even if there are 0 arguments).
Related
I am making a program that works on chat files under the following general form:
Open file & import lines (via readlines)
Do an initial pass to turn the list of strings into better-formed data (currently dicts) by:
Throwing out out malformed lines
Separating out the usernames from the text of the message
Throwing out lines for ignored (typically bot) users
Marking which lines are /me commands
Do a second pass over the list of dicts to apply various manipulations on them, such as:
Replacing every mention of a nick with its alias
Applying special formatting to /me commands
Rather than have multiple switches in the config file and lots of if statement checks within the loops, I believe the program would be cleaner if I generated the list of functions elsewhere and then fed the program the list of dicts (or strings, depending on which part of the program I'm at) and a list of functions such that the list of functions gets applied to each of the items in the list of objects.
It seems that this probably would be a good case for list comprehensions if I were only applying a single function to each item, but I don't want to have to do a separate pass through the log for every function that I want to call. However, this answer notes that list comprehension probably aren't what I want, since they return a completely new list, rather than modifying in place.
Is my best option to have two variants of the following?
for item in list:
item = a(b(c(d(item, dparam1, dparam2), cparam)), aparams)
(for readability, I'd put each function on its own line, like:
for item in list:
item = d(item, dparam1, dparam2)
item = c(item, cparam)
item = b(item)
item = a(item, aparams)
However, the above doesn't eliminate the need for if checks on all the switches and wouldn't allow for applying function a at two different places unless I explicitly add a switch to do so.
Based on your sample code, you may try this way,
func_list = [d, c, b, a]
for idx, item in enumerate(item_list):
item_list[idx] = reduce(lambda v, func: func(v), func_list, item)
Let each func handle the data, make the loop more like pipeline.
I have a dictionary which contains (roughly) 6 elements, each of an element which looks like the following:
What I want to do is find a particular domain (that I pass through a method) and if it exists, it stores the keyword and its position within an object. I have tried the following
def parseGoogleResponse(response, website):
i = 0
for item in response['items']:
if(item['formattedUrl'] == website):
print i
break;
i++
This approach seems to be a bit tedious and also i also remains the same at i = 10 and I'm pretty sure that this is a more efficient way. I also have to keep in consideration that if the website is not found the first time, it then queries the API for a maximum up to 5 pages, each page contains 6 search results so I somehow have to calculate the position if it is on a different page.
Any ideas
Dictionaries in Python are not ordered. There is no way to find something's position in a dictionary, unlike list type objects.
You can rather easily check for the existence of a value in the dictionary with something like:
if website in response['items'].values():
# If you enter this section, you know it's in the dictionary
else:
# If you end up here, it isn't in the dictionary
I'm working with the Flask framework in Python, and need to hand off a list of lists to a renderer.
I step through a loop and create a list, sort it, append it to another list, then call the render function with the masterlist, like so:
for itemID in itemsArray:
avgQuantity = getJitaQuantity(itemID)
lowestJitaSell = getJitaLowest(itemID)
candidateArray = findLowestPrices(itemID, lowestJitaSell, candidateArray, avgQuantity)
candidateArray.sort()
multiCandidateArray.append(candidateArray)
renderPage(multiCandidateArray)
My problem is that I need to clear the candidateArray and create a new one each time through the loop, but it looks like the candidateArray that I append to the multiCandidateArray is actually a pointer, not the values themselves.
When I do this:
for itemID in itemsArray:
avgQuantity = getJitaQuantity(itemID)
lowestJitaSell = getJitaLowest(itemID)
candidateArray = findLowestPrices(itemID, lowestJitaSell, candidateArray, avgQuantity)
candidateArray.sort()
multiCandidateArray.append(candidateArray)
**del candidateArray[:]**
renderPage(multiCandidateArray)
I end up with no values.
Is there a way to handle this situation that I'm missing?
I would probably go with something like:
for itemID in itemsArray:
avgQuantity = getJitaQuantity(itemID)
lowestJitaSell = getJitaLowest(itemID)
candidateArray = findLowestPrices(itemID, lowestJitaSell, candidateArray, avgQuantity)
multiCandidateArray.append(sorted(candidateArray))
No need to del anything here, and sorted returns a new list, so even if FindLowestPrices is for some reason returning references to the same list (which is unlikely), then you'll still have unique lists in the multiCandidateArray (although your unique lists could hold references to the same objects).
Your code already creates a new one each time through the loop.
candidateArray = findLowestPrices(...)
This assigns a new list to the variable, candidateArray. It should work fine.
When you do this:
del candidateArray[:]
...you're deleting the contents of the same list you just appended to the master list.
Don't think about pointers or variables; just think about objects, and remember nothing in Python is ever implicitly copied. A list is an object. At the end of the loop, candidateArray names the same list object as multiCandidateArray[-1]. They're different names for the same thing. On the next run through the loop, candidateArray becomes a name for a new list as produced by findLowestPrices, and the list at the end of the master list is unaffected.
I've written about this before; the C way of thinking about variables as being predetermined blocks of memory just doesn't apply to Python at all. Names are moved onto values, rather than values being copied into some fixed number of buckets.
(Also, nitpicking, but Python code generally uses under_scores and doesn't bother with types in names unless it's really ambiguous. So you might have candidates and multi_candidates. Definitely don't call anything an "array", since there's an array module in the standard library that does something different and generally not too useful. :))
I am writing a program in python and I am using a dictionary. I need to create an empty list for each key in the dictionary, and each list needs to have the same name as the key. The keys are user entered, which is why I can't just make a list in the conventional way.
This was the first thing I tried
a = {"x":1, "y":2, "z"3}
list(a.keys())
a.pop() = [] # This raises an error
I also tried to make the lists when the dictionary was being created, but this did not work either:
a = {}
b = input("INPUT1")
c = input("INPUT2")
a[b] = c
b = []
This created a list with the name "b" rather than whatever the user entered. Please help!!
This really doesn't make much sense. Why do your lists need 'names'? For that matter, what do you mean by 'names'?
Secondly, your code doesn't do anything. a.keys() is already a list. Calling list on it doesn't do anything else. But in any case, whatever the result of that line is, it is immediately thrown away, as you don't store the result anywhere.
pop doesn't work on dictionaries, it works on lists. And what does it mean to set the result of pop to a list? Are you trying to dynamically create a set of local variables with the names of each key in the dictionary? If so, why? Why not simply create another dictionary with the keys of the first, and each value as a new list? That can be done in one command:
b = dict((k, []) for k in b.keys())
(Note that dict.fromkeys() won't work here, as that would cause each element to share the same list.)
Use raw_input instead. input expects a valid Python expression and WILL evaluate whatever the user inputs. So if the user inputs a word, it'll evaluate that word and try to find an object with its name.
EDIT: for further clarification, input("INPUT1") is the equivalent of doing eval(raw_input("INPUT1")), for instance.
I have the following snippet of code. I'm basically trying to get the index/iterator of a particular string in a list (aside from just knowing whether it is present). Is this possible at all, or should I be using a loop-with-an-if?
bucket = ["alpha", "beta", "gamma"]
content = ""
if any(content == "beta" for content in bucket):
print content
Having 'content' as global or simply within the loop did not make a difference
Generator expressions do not leak the iterator. List comprehensions in 2.x do, but not in 3.x.
You are creating a generator for searching within the any call. That generator as you have left it is a temporary. That is, it exists only within the call to any so you will not be able to look at it afterwards. If you want it to come out to the location of the index then do this:
item = [x for x in enumerate(bucket) if x[1] == "beta"]
which generates the list of all items which match plus the indexes.