I have a list like this:
data.append(
{
"type": type,
"description": description,
"amount": 1,
}
)
Every time there is a new object I want to check if there already is an entry in the list with the same description. If there is, I need to add 1 to the amount.
How can I do this the most efficient? Is the only way going through all the entries?
I suggest making data a dict and using the description as a key.
If you are concerned about the efficiency of using the string as a key, read this: efficiency of long (str) keys in python dictionary.
Example:
data = {}
while loop(): # your code here
existing = data.get(description)
if existing is None:
data[description] = {
"type": type,
"description": description,
"amount": 1,
}
else:
existing["amount"] += 1
In either case you should first benchmark the two solutions (the other one being the iterative approach) before reaching any conclusions about efficiency.
I'm trying to create if block in my python3 script that checks if a value exists within a list I pull from JSON. The JSON data is below:
[
{
"id": 59616405645,
"name": "Foo"
},
{
"id": 990164054345,
"name": "FindMe"
},
{
"id": 2009167874,
"name": "Bar"
}
]
I'm trying to determine whether or not the value of Bar exists within the list. To do so I'm doing the following which directly references the index:
if "FindMe" in m_orgs[1].values():
print("Yo it's here")
else:
print("Yo it's not here.")
But the JSON data I'm pulling will always have different results and we will never know the index numbers, so direct reference will not work. How do I reference all indexes in a list at once?
You can't reference all indexes at once, but you can loop through them, and stop as soon as you find the first existence. Something like:
found = any("findMe" in item.values() for item in m_orgs)
This line will stop the execution when it finds the first True value. So worst case, it will look through every position and not find anything.
You can use any() like this:
if any(d['name'] == 'Foo' for d in json):
do this
You can first translate the original json data to set of data, and then simply check through set operations,
name_set = {org['name'] for org in m_orgs}
print 'FindMe' in name_set
I'm having troubles parsing a complicated json. That is it:
{
"response": {
"players": [
{
"bar": "76561198034360615",
"foo": "49329432943232423"
}
]
}
}
My code:
url = urllib.urlopen("foobar").read()
js = json.load(url)
data = js['response']
print data['players']
The problem is that this would print the dict. What I want is to reach the key's values, like foo and bar. What I tried so far is doing data['players']['foo'] and it gives me an error that list indices should be integers, I tried of course, it didn't work. So my question is how do I reach these values? Thanks in advance.
data['response']['players'] is an array (as defined by the brackets ([, ]), so you need to access items using a specific index (0 in this case):
data['players'][0]['foo']
Or iterate over all players:
for player in data['response']['players']:
print player['foo']
The problem is that players is a list of items ([ ] in json). So you need to select the first and only item in this case using [0].
print data['players'][0]['foo']
But, keep in mind that you may have more than one player, in which case you either need to specify the player, or loop through the players using a for loop
for player in data['players']:
print player['foo']
I have python list like below:
DEMO_LIST = [
[{'unweighted_criket_data': [-46.14554728131345, 2.997789122813151, -23.66171024766996]},
{'weighted_criket_index_input': [-6.275794430258629, 0.4076993207025885, -3.2179925936831144]},
{'manual_weighted_cricket_data': [-11.536386820328362, 0.7494472807032877, -5.91542756191749]},
{'average_weighted_cricket_data': [-8.906090625293496, 0.5785733007029381, -4.566710077800302]}],
[{'unweighted_football_data': [-7.586729834820534, 3.9521665714843675, 5.702038461085529]},
{'weighted_football_data': [-3.512655913521907, 1.8298531225972623, 2.6400438074826]},
{'manual_weighted_football_data': [-1.8966824587051334, 0.9880416428710919, 1.4255096152713822]},
{'average_weighted_football_data': [-2.70466918611352, 1.4089473827341772, 2.0327767113769912]}],
[{'unweighted_rugby_data': [199.99999999999915, 53.91020408163265, -199.9999999999995]},
{'weighted_rugby_data': [3.3999999999999857, 0.9164734693877551, -3.3999999999999915]},
{'manual_rugby_data': [49.99999999999979, 13.477551020408162, -49.99999999999987]},
{'average_weighted_rugby_data': [26.699999999999886, 7.197012244897959, -26.699999999999932]}],
[{'unweighted_swimming_data': [2.1979283454982053, 14.079951031527246, -2.7585499298828777]},
{'weighted_swimming_data': [0.8462024130168091, 5.42078114713799, -1.062041723004908]},
{'manual_weighted_swimming_data': [0.5494820863745513, 3.5199877578818115, -0.6896374824707194]},
{'average_weighted_swimming_data': [0.6978422496956802, 4.470384452509901, -0.8758396027378137]}]]
I want to manipulate list items and do some basic math operation,like getting each data type list (example taking all first element of unweighted data and do sum etc)
Currently I am doing it like this.
The current solution is a very basic one, I want to do it in such way that if the list length is grown, it can automatically calculate the results. Right now there are four list, it can be 5 or 8,the final result should be the summation of all the first element of unweighted values,example:
now I am doing result_u1/4,result_u2/4,result_u3/4
I want it like result_u0/4,result_u1/4.......result_n4/4 # n is the number of list inside demo list
Any idea how I can do that?
(sorry for the beginner question)
You can implement a specific list class for yourself, that adds your summary with new item's values in append function, or decrease them on remove:
class MyList(list):
def __init__(self):
self.summary = 0
list.__init__(self)
def append(self, item):
self.summary += item.sample_value
list.append(self, item)
def remove(self, item):
self.summary -= item.sample_value
list.remove(self, item)
And a simple usage:
my_list = MyList()
print my_list.summary # Outputs 0
my_list.append({'sample_value': 10})
print my_list.summary # Outputs 10
In Python, whenever you start counting how many there are of something inside an iterable (a string, a list, a set, a collection of any of these) in order to loop over it - its a sign that your code can be revised.
Things can can work for 3 of something, can work for 300, 3000 and 3 million of the same thing without changing your code.
In your case, your logic is - "For every X inside DEMO_LIST, do something"
This translated into Python is:
for i in DEMO_LIST:
# do something with i
This snippet will run through any size of DEMO_LIST and each time i is each of whatever is in side DEMO_LIST. In your case it is the list that contains your dictionaries.
Further expanding on that, you can say:
for i in DEMO_LIST:
for k in i:
# now you are in each list that is inside the outer DEMO_LIST
Expanding this to do a practical example; a sum of all unweighted_criket_data:
all_unweighted_cricket_data = []
for i in DEMO_LIST:
for k in i:
if 'unweighted_criket_data' in k:
for data in k['unweighted_cricket_data']:
all_unweighted_cricked_data.append(data)
sum_of_data = sum(all_unweighted_cricket_data)
There are various "shortcuts" to do the same, but you can appreciate those once you understand the "expanded" version of what the shortcut is trying to do.
Remember there is nothing wrong with writing it out the 'long way' especially when you are not sure of the best way to do something. Once you are comfortable with the logic, then you can use shortcuts like list comprehensions.
Start by replacing this:
for i in range(0,len(data_list)-1):
result_u1+=data_list[i][0].values()[0][0]
result_u2+=data_list[i][0].values()[0][1]
result_u3+=data_list[i][0].values()[0][2]
print "UNWEIGHTED",result_u1/4,result_u2/4,result_u3/4
With this:
sz = len(data_list[i][0].values()[0])
result_u = [0] * sz
for i in range(0,len(data_list)-1):
for j in range(0,sz):
result_u[j] += data_list[i][0].values()[0][j]
print "UNWEIGHTED", [x/len(data_list) for x in result_u]
Apply similar changes elsewhere. This assumes that your data really is "rectangular", that is to say every corresponding inner list has the same number of values.
A slightly more "Pythonic"[*] version of:
for j in range(0,sz):
result_u[j] += data_list[i][0].values()[0][j]
is:
for j, dataval in enumerate(data_list[i][0].values()[0]):
result_u[j] += dataval
There are some problems with your code, though:
values()[0] might give you any of the values in the dictionary, since dictionaries are unordered. Maybe it happens to give you the unweighted data, maybe not.
I'm confused why you're looping on the range 0 to len(data_list)-1: if you want to include all the sports you need 0 to len(data_list), because the second parameter to range, the upper limit, is excluded.
You could perhaps consider reformatting your data more like this:
DEMO_LIST = {
'cricket' : {
'unweighted' : [1,2,3],
'weighted' : [4,5,6],
'manual' : [7,8,9],
'average' : [10,11,12],
},
'rugby' : ...
}
Once you have the same keys in each sport's dictionary, you can replace values()[0] with ['unweighted'], so you'll always get the right dictionary entry. And once you have a whole lot of dictionaries all with the same keys, you can replace them with a class or a named tuple, to define/enforce that those are the values that must always be present:
import collections
Sport = collections.namedtuple('Sport', 'unweighted weighted manual average')
DEMO_LIST = {
'cricket' : Sport(
unweighted = [1,2,3],
weighted = [4,5,6],
manual = [7,8,9],
average = [10,11,12],
),
'rugby' : ...
}
Now you can replace ['unweighted'] with .unweighted.
[*] The word "Pythonic" officially means something like, "done in the style of a Python programmer, taking advantage of any useful Python features to produce the best idiomatic Python code". In practice it usually means "I prefer this, and I'm a Python programmer, therefore this is the correct way to write Python". It's an argument by authority if you're Guido van Rossum, or by appeal to nebulous authority if you're not. In almost all circumstances it can be replaced with "good IMO" without changing the sense of the sentence ;-)
I'd like to:
Check a key / value at position i
Check to see if key / value contains a string
delete / store in another variable either the key / value
The equivelant of this Java code:
//Some list...
ArrayList<String> example;
...
//Index into data structure
example.get(i);
//Check for some string...
if (example.get(i).contains("someText")){
somestuff;
}
//Store in some other variable
exam = example.get(i)
That's what I'm effectively trying to in Java, however I'd like to be able to do that with Python dictionarties however I'm not sure if this is possible, as I find the Python documentation rather hard to read.
Python dictionaries are implemented as hash tables, so there is no intrinsic ordering; therefore, "position i" is a totally nonsensical concept for a dict -- it's like asking for the dict entry that's most yellow, or that least resembles a llama... those concepts just don't apply to dict entries, and "position i" is just as totally inapplicable.
Where does that i come from, i.e., what's the real issue you're trying to solve? If your requirement is to iterate over the dictionary, you do that directly, without the crutch of a "numeric index". Or, if you do need to keep some specific order or other, then you don't use a dict, but rather some different data structure. If you explain exactly the purpose you're trying to address, I'm sure we can help you.
Direct translation (for an ArrayList<String>, you do not want a dictionary, you want a list):
example = ["foo", "bar", "baz"]
str = example[i]
if "someText" in str:
somestuff()
Get used to the for keyword, though, it's awesome in Python:
for str in example:
if "someText" in str:
someStuff()
Here's an example using dictionaries:
fruits = {
"apple": "red",
"orange": "orange",
"banana": "yellow",
"pear": "green"
}
for key in fruits:
if fruits[key] == "apple":
print "An apple is my favorite fruit, and it is", fruits[key]
else:
print "A", key, "is not my favorite fruit, and it is", fruits[key]
Iteration using for on a dictionary results in the keys, it's still up to you to index the item itself. As Alex pointed out, we're really off-base answering you with so little information, and it sounds like you're not well-rooted in data structures (dictionaries will probably yield a different order every time you iterate it).
Yo can do that to reproduce the same behavior that your example in Java.
# Some list
example = {} # or example = dict()
...
# Index into data estructure.
example[example.keys(i)]
# Check for some string...
if example[example.keys(i)] == 'someText' :
pass
# Store in some other variable...
exam = example[example.keys(i)]
del example[example.keys(i)]
# ...or
exam = example.pop(example.keys(i))
What's nice about Python is that you can try code interactively.
So we create a list which is like a Java List:
>>> mylist = ["python","java","ruby"]
>>> mylist
['python', 'java', 'ruby']
We can get an entry in the list via its index:
>>> mylist[0]
'python'
And use the find function to search for substrings:
>>> mylist[1].find("av")
1
>>> mylist[1].find("ub")
-1
It returns -1 if the string isn't found.
Copying an entry to a new variable is done just how you'd expect:
>>> newvalue = mylist[2]
>>> newvalue
'ruby'
Or we can create a dict which is like a Java Map, storing by key rather than index, but these work very similarly to lists in Python:
>>> mydict = { 'python':'Guido', 'java':'James', 'ruby':'Yukihiro' }
>>> mydict['java']
'James'
>>> othervalue = mydict['ruby']
>>> othervalue
'Yukihiro'
>>> mydict['python'].find('uid')
1
>>> mydict['python'].find('hiro')
-1
>>> mydict['ruby'].find('hiro')
4