list-comprehension

问题 I have a list of lists of tuples, where every tuple is of equal length, and I need to convert the tuples to a Pandas dataframe in such a way that the columns of the dataframe are equal to the length of the tuples, and each tuple item is a row entry across the columns. I have consulted other questions on this topic (e.g., Convert a list of lists of tuples to pandas dataframe, List of list of tuples to pandas dataframe, split list of tuples in lists of list of tuples) unsuccessfully. The

问题 I have a list of lists of tuples, where every tuple is of equal length, and I need to convert the tuples to a Pandas dataframe in such a way that the columns of the dataframe are equal to the length of the tuples, and each tuple item is a row entry across the columns. I have consulted other questions on this topic (e.g., Convert a list of lists of tuples to pandas dataframe, List of list of tuples to pandas dataframe, split list of tuples in lists of list of tuples) unsuccessfully. The

问题 This question already has answers here : How do you remove duplicates from a list whilst preserving order? (32 answers) Closed 27 days ago . I've just started learning python few weeks ago. I'm trying to convert this for loop to a list comprehension. The goal is to retrieve all values with USA as a key. Here's my code: countries = {'Beijing':{'China':51, 'USA':36, 'Russia':22, 'Great Britain':19}, 'London':{'USA':46, 'China':38, 'Great Britain':29, 'Russia':22}, 'Rio':{'USA':35, 'Great

问题 This question already has answers here : How do you remove duplicates from a list whilst preserving order? (32 answers) Closed 27 days ago . I've just started learning python few weeks ago. I'm trying to convert this for loop to a list comprehension. The goal is to retrieve all values with USA as a key. Here's my code: countries = {'Beijing':{'China':51, 'USA':36, 'Russia':22, 'Great Britain':19}, 'London':{'USA':46, 'China':38, 'Great Britain':29, 'Russia':22}, 'Rio':{'USA':35, 'Great

问题 This question already has answers here : How do you remove duplicates from a list whilst preserving order? (32 answers) Closed 27 days ago . I've just started learning python few weeks ago. I'm trying to convert this for loop to a list comprehension. The goal is to retrieve all values with USA as a key. Here's my code: countries = {'Beijing':{'China':51, 'USA':36, 'Russia':22, 'Great Britain':19}, 'London':{'USA':46, 'China':38, 'Great Britain':29, 'Russia':22}, 'Rio':{'USA':35, 'Great

问题 I have a list of Persona models being returned in p.followings and I want to extract the followed_id field from this list of models into a separate list. p.followings returns... [ %Poaster.Personas.Following{ __meta__: #Ecto.Schema.Metadata<:loaded, "followings">, followed: %Poaster.Personas.Persona{ __meta__: #Ecto.Schema.Metadata<:loaded, "personas">, background_image_url: nil, bio: "ASDF", followings: #Ecto.Association.NotLoaded<association :followings is not loaded>, id: 42, inserted_at:

问题 This question is related to my previous question and Bill's response there. I have a class named StrucData in subfile.py class StrucData: def __init__(self, name): self.name=name def loadData(self, size=1, cost=1): self.size=size self.cost=cost return self In the main file I: call the subfile, create a list of data names loop through the list to instantiate the objects; and load data using 'loadData' method for each object (I'm using the same 'size' and 'cost' to make this example easy.) in

问题 I wrote a simple script that test the speed and this is what I found out. Actually for loop was fastest in my case. That really suprised me, check out bellow (was calculating sum of squares). Is that because it holds list in memory or is that intended? Can anyone explain this. from functools import reduce import datetime def time_it(func, numbers, *args): start_t = datetime.datetime.now() for i in range(numbers): func(args[0]) print (datetime.datetime.now()-start_t) def square_sum1(numbers):

问题 I'm using the following list comprehension: resources = [obj.get("file") for obj in iterator if obj.get("file") != None] Is there a way to "cache" the value of obj.get("file") when it's checked in the if statement so that it doesn't have to call get again on obj when it generates the return list? 回答1: If you want to stay with list / iterator comprehensions instead of using filter you can simply use: resources = [file_obj for file_obj in (obj.get("file") for obj in iterator) if file_obj is not

问题 I'm using the following list comprehension: resources = [obj.get("file") for obj in iterator if obj.get("file") != None] Is there a way to "cache" the value of obj.get("file") when it's checked in the if statement so that it doesn't have to call get again on obj when it generates the return list? 回答1: If you want to stay with list / iterator comprehensions instead of using filter you can simply use: resources = [file_obj for file_obj in (obj.get("file") for obj in iterator) if file_obj is not