class Websites
default = 'https://google.com'
spotify = 'https://spotify.com'
facebook = 'https://facebook.com'
twitter = 'https://twitter.com'
[...]
from websites import Websites
random_website = random.choice(list(vars(Websites).values()))
browser.get(random_website) # This line fails like 30-50% of the time
Note that I am purposefully not using a dictionary here, because I would like to use the random value to get the key.
Debugging, I've found that it will randomly get set to something like this:
random_website = {getset_descriptor} <attribute '__dict__' of 'Websites' objects>
I'm really not sure why it wouldn't be working, because I've tested all of the URLs multiple times.
Also note that this application uses threads -- there are multiple instances of this application (usually 4) and at any given time roughly 1-2 fail, in case that might matter. I'm still very new to Python and Selenium (and still not that experienced in coding, honestly). Please let me know if I can provide more information that might be helpful.
vars(Websites)
is a dictionary
has all kinds of objects in it, mostly inherited from object
If you print it, you will see all kinds of things like unbound methods and other normal object attributes. This happens because an object's __dict__ automatically gets some default elements assigned by the type metaclass. All these attributes should be dunders.
You therefore have two options:
Persist in your current course and filter for dunders:
items = [v for k, v in vars(Website).items() if not k.startswith('__')]
This is not the recommended approach.
Just use a normal dictionary that only contains what you want. You're calling values on it either way. If you don't really need the labels, just use a list.
You laid out your thought process pretty clearly in the comments to Mad Physicists's answer so you just need a mini-tutorial in Python.
A. How to store the data. As suggested above, a dictionary is probably the best way, with strings as keys and values. You probably want to deal with strings, not with variables.
websites = {'default':'https://www.google.com', 'stack':'https://stackoverflow.com'}
B. You can get a list of all the keys in the dictionary, or a list of (key, value) pairs called tuples. This means replacing vars(Websites).values() with websites.keys() or websites.items(). Then your code will give you a random key or item.
C. If you chose ```keys()``, then you can just print the random thing you got, and use that key to get the corresponding value from the dictionary.
random_key = random.choice(websites.keys())
print(random_key)
random_website = websites[random_key] # this is how you get values using keys
D. If you chose items(), then the tuple you got is basically an immutable list (you can't change or assign to either value). You can pull them out by specifying an index in the list. Python indices start at 0.
random_item = random.choice(websites.items())
print(random_item) # something like ('default', 'https://www.google.com')
random_key = random_item[0] # this is how you choose an item from a list or tuple
print(random_key)
random_website = random_item[1]
Related
I am new to Python from R. I have recently spent a lot of time reading up on how everything in Python is an object, objects can call methods on themselves, methods are functions within a class, yada yada yada.
Here's what I don't understand. Take the following simple code:
mylist = [3, 1, 7]
If I want to know how many times the number 7 occurs, I can do:
mylist.count(7)
That, of course, returns 1. And if I want to save the count number to another variable:
seven_counts = mylist.count(7)
So far, so good. Other than the syntax, the behavior is similar to R. However, let's say I am thinking about adding a number to my list:
mylist.append(9)
Wait a minute, that method actually changed the variable itself! (i.e., "mylist" has been altered and now includes the number 9 as the fourth digit in the list.) Assigning the code to a new variable (like I did with seven_counts) produces garbage:
newlist = mylist.append(9)
I find the inconsistency in this behavior a bit odd, and frankly undesirable. (Let's say I wanted to see what the result of the append looked like first and then have the option to decide whether or not I want to assign it to a new variable.)
My question is simple:
Is there a way to know in advance if calling a particular method will actually alter your variable (object)?
Aside from reading the documentation (which for some methods will include type annotations specifying the return value) or playing with the method in the interactive interpreter (including using help() to check the docstring for a type annotation), no, you can't know up front just by looking at the method.
That said, the behavior you're seeing is intentional. Python methods either return a new modified copy of the object or modify the object in place; at least among built-ins, they never do both (some methods mutate the object and return a non-None value, but it's never the object just mutated; the pop method of dict and list is an example of this case).
This either/or behavior is intentional; if they didn't obey this rule, you'd have had an even more confusing and hard to identify problem, namely, determining whether append mutated the value it was called on, or returned a new object. You definitely got back a list, but is it a new list or the same list? If it mutated the value it was called on, then
newlist = mylist.append(9)
is a little strange; newlist and mylist would be aliases to the same list (so why have both names?). You might not even notice for a while; you'd continue using newlist, thinking it was independent of mylist, only to look at mylist and discover it was all messed up. By having all such "modify in place" methods return None (or at least, not the original object), the error is discovered more quickly/easily; if you try and use newlist, mistakenly believing it to be a list, you'll immediately get TypeErrors or AttributeErrors.
Basically, the only way to know in advance is to read the documentation. For methods whose name indicates a modifying operation, you can check the return value and often get an idea as to whether they're mutating. It helps to know what types are mutable in the first place; list, dict, set and bytearray are all mutable, and the methods they have that their immutable counterparts (aside from dict, which has no immutable counterpart) lack tend to mutate the object in place.
The default tends to be to mutate the object in place simply because that's more efficient; if you have a 100,000 element list, a default behavior for append that made a new 100,001 element list and returned it would be extremely inefficient (and there would be no obvious way to avoid it). For immutable types (e.g. str, tuple, frozenset) this is unavoidable, and you can use those types if you want a guarantee that the object is never mutate in place, but it comes at a cost of unnecessary creation and destruction of objects that will slow down your code in most cases.
Just checkout the doc:
>>> list.count.__doc__
'L.count(value) -> integer -- return number of occurrences of value'
>>> list.append.__doc__
'L.append(object) -> None -- append object to end'
There isn't really an easy way to tell, but:
immutable object --> no way of changing through method calls
So, for example, tuple has no methods which affect the tuple as it is unchangeable so methods can only return new instances.
And if you "wanted to see what the result of the append looked like first and then have the option to decide whether or not I want to assign it to a new variable" then you can concatenate the list with a new list with one element.
i.e.
>>> l = [1,2,3]
>>> k = l + [4]
>>> l
[1, 2, 3]
>>> k
[1, 2, 3, 4]
Not from merely your invocation (your method call). You can guarantee that the method won't change the object if you pass in only immutable objects, but some methods are defined to change the object -- and will either not be defined for the one you use, or will fault in execution.
I Real Life, you look at the method's documentation: that will tell you exactly what happens.
[I was about to include what Joe Iddon's answer covers ...]
I was thinking about parts of my class api's and one thing that came up was the following:
Should I use a tuple/list of equal attributes or should I use several attributes, e.g. let's say I've got a Controller class which reads several thermometers.
class Controller(object):
def __init__(self):
self.temperature1 = Thermometer()
self.temperature3 = Thermometer()
self.temperature2 = Thermometer()
self.temperature4 = Thermometer()
vs.
class Controller(object):
def __init__(self):
self.temperature = tuple(Thermometer() for _ in range(4))
Is there a best practice when I should use which style?
(Let's assume the number of Thermometers will not be changed, otherwise choosing the second style with a list would be obvious.)
A tuple or list, 100%. variable1, variable2, etc... is a really common anti-pattern.
Think about how you code later - it's likely you'll want to do similar things to these items. In a data structure, you can loop over them to perform operations, with the numbered variable names, you'll have to do it manually. Not only that but it makes it easier to add in more values, it makes you code more generic and therefore more reusable, and means you can add new values mid-execution easily.
Why make the assumption the number will not be changed? More often than not, assumptions like that end up being wrong. Regardless, you can already see that the second example exemplifies the do not repeat yourself idiom that is central to clear, efficient code.
Even if you had more relevant names eg: cpu_temperature, hdd_temperature, I would say that if you ever see yourself performing the same operations on them, you want a data structure, not lots of variables. In this case, a dictionary:
temperatures = {
"cpu": ...,
"hdd": ...,
...
}
The main thing is that by storing the data in a data structure, you are giving the software the information about the grouping you are providing. If you just give them the variable names, you are only telling the programmer(s) - and if they are numbered, then you are not even really telling the programmer(s) what they are.
Another option is to store them as a dictionary:
{1: temp1, 2: temp2}
The most important thing in deciding how to store data is relaying the data's meaning, if these items are essentially the same information in a slightly different context then they should be grouped (in terms of data-type) to relay that - i.e. they should be stored as either a tuple or a dictionary.
Note: if you use a tuple and then later insert more data, e.g. a temp0 at the beginning, then there could be backwards-compatability issues where you've grabbed individual variables. (With a dictionary temp[1] will always return temp1.)
How can I store values in a list without specifying index numbers?
For example
outcomeHornFive=5
someList = []
someList.append(outComeHornFive)
instead of doing this,
someList[0] # to reference horn five outcome
how can i do something like this? The reason is there are many items that I need to reference within the list and I just think it's really inconvenient to keep track of which index is what.
someList.hornFive
You can use another data structure if you'd like to reference things by attribute access (or otherwise via a name).
You can put them in a dict, or create a class, or do something else. It depends what kind of other interaction you want to have with that object.
(P.S., we call those lists, not arrays).
Instead of using a list you can use a dictionary.
See data types in the python documentation.
A dictionary allows you to lookup a value using a key:
my_dict["HornFive"] = 20
You cannot and you shouldn't. If you could do that, how would you refer to the list itself? And you will need to refer to the list itself.
The reason is there are many items that i need to reference within the list and I just think it's really inconvenient to keep track of which index is what.
You'll need to do something of that ilk anyway, no matter how you organize your data. If you had separate variables, you'd need to know which variable stores what. If you had your way with this, you'd still need to know that a bare someList refers to "horn five" and not to, say, "horn six".
One advantage of lists and dicts is that you can factor out this knowledge and write generic code. A dictionary, or even a custom class (if there is a finite number of semantically distinct attributes, and you'd never have to use it as a collection), may help with the readability by giving it an actual name instead of a numeric index.
referenced from http://parand.com/say/index.php/2008/10/13/access-python-dictionary-keys-as-properties/
Say you want to access the values if your dictionary via the dot notation instead of the dictionary syntax. That is, you have:
d = {'name':'Joe', 'mood':'grumpy'}
And you want to get at “name” and “mood” via
d.name
d.mood
instead of the usual
d['name']
d['mood']
Why would you want to do this? Maybe you’re fond of the Javascript Way. Or you find it more aesthetic. In my case I need to have the same piece of code deal with items that are either instances of Django models or plain dictionaries, so I need to provide a uniform way of getting at the attributes.
Turns out it’s pretty simple:
class DictObj(object):
def __init__(self, d):
self.d = d
def __getattr__(self, m):
return self.d.get(m, None)
d = DictObj(d)
d.name
# prints Joe
d.mood
# prints grumpy
I have the following in a Python script:
setattr(stringRESULTS, "b", b)
Which gives me the following error:
AttributeError: 'str' object has no attribute 'b'
Can any-one telling me what the problem is here?
Don't do this. To quote the inestimable Greg Hewgill,
"If you ever find yourself using quoted names to refer to variables,
there's usually a better way to do whatever you're trying to do."
[Here you're one level up and using a string variable for the name, but it's the same underlying issue.] Or as S. Lott followed up with in the same thread:
"90% of the time, you should be using a dictionary. The other 10% of
the time, you need to stop what you're doing entirely."
If you're using the contents of stringRESULTS as a pointer to some object fred which you want to setattr, then these objects you want to target must already exist somewhere, and a dictionary is the natural data structure to store them. In fact, depending on your use case, you might be able to use dictionary key/value pairs instead of attributes in the first place.
IOW, my version of what (I'm guessing) you're trying to do would probably look like
d[stringRESULTS].b = b
or
d[stringRESULTS]["b"] = b
depending on whether I wanted/needed to work with an object instance or a dictionary would suffice.
(P.S. relatively few people subscribe to the python-3.x tag. You'll usually get more attention by adding the bare 'python' tag as well.)
Since str is a low-level primitive type, you can't really set any arbitrary attribute on it. You probably need either a dict or a subclass of str:
class StringResult(str):
pass
which should behave as you expect:
my_string_result = StringResult("spam_and_eggs")
my_string_result.b = b
EDIT:
If you're trying to do what DSM suggests, ie. modify a property on a variable that has the same name as the value of the stringRESULTS variable then this should do the trick:
locals()[stringRESULTS].b = b
Please note that this is an extremely dangerous operation and can wreak all kinds of havoc on your app if you aren't careful.
I am trying to create a small server type application and have a question regarding organizing data with dicts. Right now I am grouping the data using the connection socket (mainly to verify where it's coming from and for sending data back out). Something like this: connected[socket] = account_data. Basically, each connected person will have account data. Since certain fields will be used a lot for comparing and checking information, such as an account ID, I want to speed things up with another dict.
For example: to find an accountID with the above method, I would have to use a for loop to go through all available connections in connected, look at the accountID in account_data for each, and then compare it. This seems to be a slow way to do it. If I could create a dict and use the accountID as the key, I think it could speed things up a little. The problem is, I plan on using 3 different dicts all ordered differently. Some data may change frequently and it seems more of a hassle to update every single dict once information changes; is there anyway to link them together?
Maybe an easier way of trying to explain what I am asking is:
You have Dict A, Dict B, Dict C, and Data. Dict A, B, and C all contain the same Data. I want it so if something changes in Data, the Data in Dict A, B, and C all change. I can of course always do dict A = data, dict B = data, etc but would get repetitive in the code after awhile. I know the data is set once the dict is created so I'm not really sure if there is a solution to this. I am just looking for advice on the best way to organize data in this situation.
First off, the data, needn't be be replicated. You can well have 3 dictionaries each using a different key, but having the same reference as its value.
Doing so you only need to change the value object once and this will be reflected in all dictionaries (or more precisely since the the dictionaries only store a reference, they'll be up to date).
Next you need to ensure "referencial integrity" i.e. if a particular record is deleted, corresponding dictionary entry needs to be be deleted in all 3 dictionaries, and, if the record gets modified, the dictionaries with a key that is now changed also need to be have the record removed and re-added under the new key. This can be done with a class that holds all 3 dictionaries and has Add(), Remove() and (if applicable) Update() methods.
Just do something like:
connected[socket] = accountids[account_data.accountid] = account_data
assuming account_data is a mutable object with attributes, this will reference that same object as a value in both dicts, with different keys of course. It doesn't have to be on one statement, i.e.:
connected[socket] = account_data
accountids[account_data.accountid] = account_data
the multiple assignments in the same statement are just a convenience; what makes it work the way you want is that Python universally operates by "object reference" (in assignments, argument passing, return statements, and so on).
If you have references to dictionaries, an update to the dictionary will be reflected to everything with a reference.
A customer connects and retains a socket, sock. You load his account and stick it in connections[sock]. Then you keep a dictionary of account IDs (the other way) with references to the accounts, accounts[account_id]. Let's try that...
connected = {}
accounts = {}
def load_account(acct):
return db_magic(acct) # Grab a dictionary from the DB
def somebody_connected(sck, acct):
global connected, accounts
account = load_account(acct)
connected[sck] = account # Now we have it by socket
accounts[acct["accountid"]] = account # Now we have it by account ID
Since we assigned account to two different places, any change to that dictionary (in either structure) will be reflected in the other. So...
def update_username(acct_id, new_username):
accounts[acct_id]["username"] = new_username
def what_is_my_username(sck):
sck.send(connected[sck]["username"]) # In response to GIMME_USERNAME
The change we execute in update_username will automatically be picked up when we do the sck.send, because the reference is exactly the same.
Maybe one of the publish/subscribe modules for Python can help you here?
See this question.