I am trying to print a list of python objects that contain a list as a property and i am having some unexpected results:
here is my code:
class video(object):
name = ''
url = ''
class topic(object):
topicName = ''
listOfVideo = []
def addVideo(self,videoToAdd):
self.listOfVideo.append(videoToAdd)
def getTopic(self):
return self.topicName
def getListOfVideo(self):
return self.listOfVideo
topic1 = topic()
topic1.topicName = 'topic1'
video1 = video()
video1.name = 'VideoName1'
video1.url = 'VideoURL1'
video2 = video()
video2.name = 'VideoName2'
video2.url = 'VideoURL2'
topic1.addVideo(video1)
topic1.addVideo(video2)
topic2 = topic()
topic2.topicName = 'topic2'
video3 = video()
video3.name = 'VideoName3'
video3.url = 'VideoURL3'
video4 = video()
video4.name = 'VideoName4'
video4.url = 'VideoURL4'
topic2.addVideo(video3)
topic2.addVideo(video4)
topicsList = []
topicsList.append(topic1)
topicsList.append(topic2)
for topicCurrent in topicsList:
print(topicCurrent.topicName)
for video in topicCurrent.getListOfVideo():
print(video.name)
print(video.url)
What I expect to get is this:
topic1
VideoName1
VideoURL1
VideoName2
VideoURL2
topic2
VideoName3
VideoURL3
VideoName4
VideoURL4
but what I actually get is this:
topic1
VideoName1
VideoURL1
VideoName2
VideoURL2
VideoName3
VideoURL3
VideoName4
VideoURL4
topic2
VideoName1
VideoURL1
VideoName2
VideoURL2
VideoName3
VideoURL3
VideoName4
VideoURL4
Why? I want to iterate over my list of topics and print out each video in each topic, but for each topic it prints out all videos???
What is going on here?
You have created class variables instead of instance variables, which are different for each instance object. Define your class as follows:
class topic(object):
def __init__(self):
self.topicName = ''
self.listOfVideo = []
def addVideo(self,videoToAdd):
self.listOfVideo.append(videoToAdd)
def getTopic(self):
return self.topicName
def getListOfVideo(self):
return self.listOfVideo
From Python Tutorial:
Instance variables are for data unique to each instance and class
variables are for attributes and methods shared by all instances of
the class.
EDIT:
One more important thing to consider is that why only listOfVideo was common for all instances but not topicName. It is because list's are mutable objects while string's are immutable.
So any changes made to listOfVideo are common for all instances, i.e., they still refer to listOfVideo defined in the topic namespace.
However when you do topic1.topicName = 'topic1', you create a new variable topicName within topic1 namespace, which overrides the topicName found in topic(class) namespace. You can confirm it by printing the value topic.topicName, which you will find to be an empty string, i.e., ''.
Related
I am leveraging the SeriesHelper object of InfluxDB library(please have a look at https://influxdb-python.readthedocs.io/en/latest/examples.html#tutorials-serieshelper) to push set of data points to InfluxDB. The SeriesHelper class has to be inherited and the child class needs to initialize various objects as its meta attributes, so as to override the default values of the objects in the Parent class.
Actual code
class MySeriesHelper(SeriesHelper):
"""Instantiate SeriesHelper to write points to the backend."""
class Meta:
"""Meta class stores time series helper configuration."""
client = myclient
series_name = 'rf_results'
fields = ['some_stat', 'other_stat']
tags = ['server_name']
bulk_size = 5
autocommit = True
Here the 'series_name' object is initialized(hard-coded) right before it is ran as a script. My use case is to initialize 'series_name' based on the runtime arguments that are passed to this script.
I tried by defining a global variable whose value is providing at runtime and assigning that global variable to the 'series_name' like the below one, but in vain.
Problematic code
series_configured = None
class MySeriesHelper(SeriesHelper):
"""Instantiate SeriesHelper to write points to the backend."""
class Meta:
"""Meta class stores time series helper configuration."""
client = myclient
series_name = series_configured
fields = ['some_stat', 'other_stat']
tags = ['server_name']
bulk_size = 5
autocommit = True
def main():
global series_configured
series_configured = args.series_name
MySeriesHelper(server_name='server_A', some_stat='Master server', other_stat='Controller')
MySeriesHelper.commit()
if __name__ == "__main__":
parser = argparse.ArgumentParser()
parser.add_argument("--series_name", dest='series_name',
help="The measurement to be used for storing the data points",required=True)
args = parser.parse_args()
main()
Error seen while running is
'NoneType' object has no attribute 'format'
It infers that the object 'series_name' is not initialized with a value. Is there any way of properly initializing it ?
When the python interpreter go over the code (line by line) it define all the classes static variable.
It's set static variable before you create an instance from a class.
That mean when you reach the point of:
autocommit = True
The value of series_name is already set to None (because that is the value of series_configured at the point).
The following example show that the static variable are already set before I created an instance:
>>> series_configured = None
>>> class MySeriesHelper:
"""Instantiate SeriesHelper to write points to the backend."""
class Meta:
"""Meta class stores time series helper configuration."""
series_name = series_configured
fields = ['some_stat', 'other_stat']
tags = ['server_name']
bulk_size = 5
autocommit = True
>>> print(MySeriesHelper.Meta.series_name)
None
If you want to change the Meta.series_configured static variable you will have to set it after the series_configured change its content.
Try the following main.
def main():
global series_configured
series_configured = args.series_name
# The following line will set the variable at the inner Meta class.
MySeriesHelper.Meta.series_name = series_configured
MySeriesHelper(server_name='server_A', some_stat='Master server', other_stat='Controller')
MySeriesHelper.commit()
I have created a script that stores and edits meta-data in a system. I am now cleaning up my code by defining a class and methods, previously I only used separate functions.
In the script I am storing old and new values of certain types of metadata in lists, which I print out after the script has completed its run. I have defined multiple lists (16 to be exact), which I realized is quite a lot when passing them through a method. I was wondering what is the most pythonic way to approach this.
These are the following list variables that i define in the beginning. In the function/method I append values to them. In the end I print the stored valued out as a report.
split_name = []
split_name_new = []
name = []
name_new = []
meta = []
meta_new = []
series = []
series_new = []
product = []
owner = []
desc = []
desc_new = []
keywords = []
keywords_new = []
no_edit_page =[]
no_edit_page_name = []
In a class i figured it will look something like (if I define all the list separately)
class Metadata_editor():
def __init__(self,url):
self.split_name = []
self.split_name_new = []
self.name = []
self.name_new = []
self.meta = []
self.meta_new = []
self.series = []
self.series_new = []
self.product = []
self.owner = []
self.desc = []
self.desc_new = []
self.keywords = []
self.keywords_new = []
self.no_edit_page =[]
self.no_edit_page_name = []
#Ugly solution because the method gets crowded by all the variables passed through
def data_edit(self, split_name, split_name_new, name, name_new,.. etc):
#Not the whole method, but just to give some idea..
#Selenium function that locates meta
md = driver.find_element_by_xpath("//input[#name='metadata-name']")
meta_data = md.get_attribute("value")
#replace_words translate the word using a dictionary object
meta_data_new = replace_words(meta_data,c)
meta.append(meta_data)
meta_new.append(meta_data_new)
The solution above I realized would not be ideal.
I found an alternative way that I could use, which is I define a list of lists. The solution would then look something like this (see below). However 'data_list[10]' is not as self-explanatory as for say 'owner'. My question is, is this the 'best' way to solve this, or do you have any other suggestions? I don't really have anything against this solution, but was wondering if there is a more 'pythonic' way to approach this.
class Metadata_editor():
def __init__(self,url):
self.data_list=[[] for _ in range(16)] #Creates a list, that contains 16 lists
# More eloquent solution, as only one variable is passed through. However finding
# the right data from data_list is perhaps not as easy before
def data_edit(self, data_list):
md = driver.find_element_by_xpath("//input[#name='metadata-name']")
meta_data = md.get_attribute("value")
meta_data_new = replace_words(meta_data,c)
data_list[5].append(meta_data)
data_list[6].append(meta_data_new)
You could store it as a dictionary. That would have the advantage of being able to reference the keys by name rather than having to remember the indexes.
class Metadata_editor():
def __init__(self, url):
keys = [
'split_name', 'split_name_new', 'name', 'name_new' 'meta', 'meta_new',
'series', 'series_new', 'product', 'owner', 'desc', 'desc_new',
'keywords', 'keywords_new', 'no_edit_page', 'no_edit_page_name',
]
self.data_dict = dict((x, []) for x in keys)
def data_edit(self):
md = driver.find_element_by_xpath("//input[#name='metadata-name']")
meta_data = md.get_attribute("value")
meta_data_new = replace_words(meta_data,c)
self.data_dict['meta'].append(meta_data)
self.data_dict['meta_new'].append(meta_data_new)
A few extra points to note:
class names generally follow the UpperCaseCamelCase convention. So Metadata_editor would more conventionally be written as MetadataEditor
Using self sets an attribute on the class, it can be accessed in the class using self and the attribute does not need to be passed into the method. I have shown this in the example above, accessing self.data_dict in the data_edit method.
You can also use setattr to set attributes to the class as shown in some of the other answers.
You can initialize multiple lists as below:
class Metadata_editor():
def __init__(self,list_names):
[setattr(self,name,[]) for name in list_names]
me = Metadata_editor(['split_name','split_name_new']) # initialize two lists
me.split_name.append(5) # add value to a list
print(me.split_name, me.split_name_new)
>>[5], [ ]
Once set as part of the class via self.list_name, the list(s) can be accessed globally within the class - no longer requiring to be 'passed in'. To initialize lists to specific values, you can do:
def __init__(self,list_names,list_values):
[setattr(self,name,value) for name,value in zip(list_names,list_values)]
Use setattr:
...
def __init__(self, url):
names = '''split_name split_name_new name
name_new meta meta_new series series_new
product owner desc desc_new keywords
keywords_new no_edit_page
no_edit_page_name'''.split()
for name in names:
setattr(self, name, [])
...
I am trying to add new objects to a class(emne) but the new instances of the class needs to be created using user input. So i need a way to be able to chose the name for the object and set some of the values of the objects with user input.
I have already tried to create a function that passes the value of the user input into a x = emner(x) to create it but it only returns:
AttributeError: 'str' object has no attribute 'fagKode'
so i think my issue is that the value of the input is created as a string so that it is not understood as a way to create the function
emne=[]
class Emne:
def __init__(self,fagKode):
self.fagKode = fagKode
self.karakter = ""
emne.append(self)
def leggTilEmne():
nyttEmne = input("test:")
nyttEmne=Emne(nyttEmne)
expected result is that the code creates a new instance of the class.
If by choosing a name you mean your fagKode attribute, what you need is:
fagKode = input('Enter code: ')
Emne(fagKode)
You're adding the instances of Enme to the list in the constructor, so you don't need to save them to a variable.
Alternatively, you can handle that in the function:
emne=[]
class Emne:
def __init__(self,fagKode):
self.fagKode = fagKode
self.karakter = ""
def leggTilEmne():
nyttEmne = input("test:")
enme.append(Emne(nyttEmne))
I'm not sure what exactly you are asking, since you haven't responded to the comments. So,
emne=[]
class Emne:
def __init__(self,fagKode):
self.fagKode = fagKode
self.karakter = ""
emne.append(self)
def leggTilEmne(self, value): # <--- is this what you want
self.nyttEmne= Emne(value)
This is an example of when to use a class method. __init__ should not be appending to a global variable, though. Either 1) have the class method append to a class attribute, or 2) have it return the object and let the caller maintain a global list.
emne = []
class Emne:
emne = []
def __init__(self, fag_kode):
self.fag_kode = fag_kode
self.karakter = ""
#classmethod
def legg_til_emne_1(cls):
nytt_emne = input("test:")
cls.emne.append(cls(nytt_emne))
#classmethod
def legg_til_emne_2(cls):
nyttEmne = input("test:")
return cls(nyttEmne)
Emne.legg_til_emne_1() # Add to Emne.emne
e = Emne.legg_til_emne_2()
emne.append(e)
I have this dictionary:
{"id":3,"name":"MySQL","description":"MySQL Database Server - Fedora 21 - medium","image":"","flavor":""}
And I have this object:
class Record():
id = None
name = None
description = None
image = None
flavor = None
How can I assign values from the dictionary to their corresponding class fields?
Take a dict object as the parameter of init function:
class Record(object):
def __init__(self,record_dict):
try:
self.id = record_dict['id']
self.name = record_dict['name']
self.description = record_dict['description']
self.image = record_dict['image']
self.flavor = record_dict['flavor']
except KeyError:
print 'KeyError'
def get_name(self):
return self.name
adict = {"id":3,"name":"MySQL","description":"MySQL Database Server - Fedora 21 - medium","image":"","flavor":""}
one_obj = Record(adict)
print one_obj
print one_obj.get_name()
output:
<__main__.Record object at 0x022E4C90>
MySQL
works for me...
You probably want something like this:
class Record:
def __init__(self, myDict):
self.id = myDict[“id”]
self.name = myDict[“name”]
self.description = myDict[“description”]
self.image = myDict[“image”]
self.flavor = myDict[“flavor”]
And call it:
rec = Record(myDict)
See here to understand the difference between class and instance variables.
Long story short, class variables have a single value for every instance of the class while instance variables values are unique to each instance.
A class variable is defined like this:
class myClass:
Classvar = ‘something’
An instance variable is defined like this:
class myClass:
def __init__():
Self.instanceVar = ‘something else’
This has already been answered here:
Convert Python dict to object?
My favorite method is this one: x.__dict__.update(d)
You can assign them as follows, assuming your dictionary name is input
id = input['id']
name = input['name']
description = input['description']
image = input['image']
flavor = input['flavor']
Try this method in which you grab the attributes of the object:
r = Record()
attributes = [i for i in dir(r) if not i.startswith('_')]
Basically, there are a bunch of background attributes that contain a bunch of underscores. The dir method gets all the attributes and we create a list of the ones that we want. At this point:
# attributes = ['count', 'description', 'flavor', 'id', 'image', 'index', 'name']
So now we use __setattr__ to set the attributes we just grabbed according to the my_dict
for i in attributes:
r.__setattr__(i, my_dict[i])
See the code run online here.
When you create the Record, pass in the dictionary. Then map the key to the value.
Another simple method, see the code here
r = Record()
for k, v in my_dict.items():
exec('r.' + k + '="' + str(v) + '"')
I really hope this is not a repeat...if it is, I can't find an answer anywhere, so I apologize.
Anyways, my question is, I'm writing code where, if the data I get requires a team instead of a player, I have a class (called Team) that holds two SinglePlayers (also a class), and then a few other attributes, just strings. The problem is, when I iterate through my loop, reading the xml data and filling up my "team" variable, it seems that all the info for the SinglePlayers doesn't get reset. This is a problem, because it is is changing that info every time I insert a new "team" into the list of "team" objects I have. The code is long, so I'm only going to post what's relevant.
I have only been working with python again for a few days. I have been working the past year in java and c++ so my brain has those concepts in my head of how variables and structures work. I know python is different, so if someone could please clarify why this doesn't work, that would be amazing. Thanks!
class SinglePlayer:
entry_code = ""
first_name = ""
last_name = ""
nation = ""
seed_rank_sgl = ""
seed_rank_dbl = ""
entry_rank_sgl = ""
entry_rank_dbl = ""
class Team:
top_player = SinglePlayer()
bottom_player = SinglePlayer()
entry_code = ""
seed_rank = ""
entry_rank = ""
def DoublesEvent(self, team_nodes):
#Create List to store team objects
teams_list = []
for k in range(0, team_nodes.length):
#Get the current node
teams_node = team_nodes.item(k)
team_node = team_nodes.item(k).getElementsByTagName("Player")
top_player_node = team_node.item(0)
bottom_player_node = team_node.item(1)
#Make a new team object to fill and add to teams_list
team = Team()
team.entry_code = teams_node.getAttribute("EntryCode")
#Top Player Info
team.top_player.first_name = top_player_node.getAttribute("FirstName")
team.top_player.last_name = top_player_node.getAttribute("LastName")
team.top_player.nation = top_player_node.getAttribute("Nation")
#Bottom Player Info
team.bottom_player.first_name = bottom_player_node.getAttribute("FirstName")
team.bottom_player.last_name = bottom_player_node.getAttribute("LastName")
team.bottom_player.nation = bottom_player_node.getAttribute("Nation")
eam.seed_rank = self.GetSeedRank(team)
team.entry_rank = self.GetEntryRank(team)
#Add the team to the list
teams_list.append(team)
return teams_list
Your class holds a reference to two SinglePlayer() instances, not your instances. Use a __init__ method to create new instances for every Team instance:
class Team:
entry_code = ""
seed_rank = ""
entry_rank = ""
def __init__(self):
self.top_player = SinglePlayer()
self.bottom_player = SinglePlayer()
As it happens, because you rebind each of the string attributes on the instances you create, you happen to create instance attributes for those. You'd be better off moving those into __init__ as well and making their relationship as instance attributes explicit:
class Team:
def __init__(self):
self.entry_code = ""
self.seed_rank = ""
self.entry_rank = ""
self.top_player = SinglePlayer()
self.bottom_player = SinglePlayer()
and do the same for your SinglePlayer class.