Develop Reference

Generating a list based on a list of dictionaries and data from another list

The following lists are given:
atr = [{'name': 'surname', 'type': 'varchar(50)', 'table': None}, {'name': 'ls_data', 'type': 'timestamp', 'table': None}, {'name': 'cpn', 'type': 'int', 'table': None}, {'name': 'code', 'type': 'varchar(200)', 'table': None}]
pk = ['surname', 'cpn', 'ls_data']
It is necessary to form a list of "type" from the atr list, while "name" from atr = pk.
The order should be as in the pk list.
Expected output
lst = ['varchar(50)', 'int', 'timestamp']
I tried it like this
lst = [d["type"] for d in atr if d["name"] in pk]
But this is incorrect, the order is not the same as in the pk list.

It would work using something like this:
lst = [atr[[d["name"] for d in atr].index(p)]["type"] for p in pk]
The output for print(lst) is:
['varchar(50)', 'int', 'timestamp']
i.e. the same result items list order as in the query items list as opposed to your original approach which gives a different order.
Though I'm not sure how readable/performant that is; it
generates a new list (only containing the values of the "name" key) from the list of dictionaries for each query item p in pk
searches for the index of the current query item p in that list
uses this index to retrieve the respective dictionary from the original atr list
and finally, select the value of the "type" key from that dictionary

Access value of a given key in a list of dictionaries

Given a list of dictionaries such as:
list_ = [
{ 'name' : 'date',
'value': '2021-01-01'
},
{ 'name' : 'length',
'value': '500'
},
{ 'name' : 'server',
'value': 'g.com'
},
How can I access the value where the key name == length?
I want to avoid iteration if possible, and just be able to check if the key called 'length' exists, and if so, get its value.

With iteration, and using next, you could do:
list_ = [
{'name': 'date',
'value': '2021-01-01'
},
{'name': 'length',
'value': '500'
},
{'name': 'server',
'value': 'g.com'
}
]
res = next(dic["value"] for dic in list_ if dic.get("name", "") == "length")
print(res)
Output
500
As an alternative, if the "names" are unique you could build a dictionary to avoid further iterations on list_, as follows:
lookup = {d["name"] : d["value"] for d in list_}
res = lookup["length"]
print(res)
Output
500
Notice that if you need a second key such as "server", you won't need to iterate, just do:
lookup["server"] # g.com

It sure is hard to find an element in a list without iterating through it. Thats the first solution I will show:
list(filter(lambda element: element['name'] == 'length', list_))[0]['value']
this will filter through your list only the elements with name 'length', choose the first from that list, then select the 'value' of that element.
Now, if you had a better data structure, you wouldn't have to iterate. In order to create that better data structure, unfortunately, we will have to iterate the list. A list of dicts with "name" and "value" could really just be a single dict where "name" is the key and "value" is the value. To create that dict:
dict_ = {item['name']:item['value'] for item in list_}
then you can just select 'length'
dict_['length']

get a value of a key associated with other key's values in dictionaries Python

I have two lists of dictionaries and json list and I need to grab a value of a specific key based on the value of a key from another dictionary. My data looks like this:
opps = [{'Product2Id': '100','Price': '1645'}, {'Product2Id': '101','Price': '5478'}]
products = [{'Id': '100', 'Name': 'Insertion'}, [{'Id': '101', 'Name': 'Print'}]
sales_json = {'Insertion': {'name': 'BAZ', 'id': '95'}, 'Print': {'name': 'BIC', 'id': '105'}
I need to loop through opps and assign a value to a new variable from sales_json. But for a specific Id that are stored in products and in opps
I tried the following:
for index, my_dict in enumerate(opps):
new_name = sales_json[products[my_dict["Product2Id"]]["Name"]]["name"]
Gives me an error.
The desired output is:
print(new_name)
BAZ,
BIC

You are trying to use the list products as a dictionary. Instead, you should first build a product number to name dictionary from it:
prod_num_to_name = {d['Id']: d['Name'] for d in products}
Then, you can run the loop you wanted, modified like this:
for index, my_dict in enumerate(opps):
new_name = sales_json[prod_num_to_name[my_dict["Product2Id"]]]["name"]
print new_name

To return a list of names that match the criteria, using a List Comprehension:
names = [ sales_json[product['Name']]['name'] for opp in opps for product in products if product['Id'] == opp['Product2Id']]
print (names)
Prints the list of names:
['BAZ', 'BIC']

Comparing values of two dictionary's items

I need to compare the values of the items in two different dictionaries.
Let's say that dictionary RawData has items that represent phone numbers and number names.
Rawdata for example has items like: {'name': 'Customer Service', 'number': '123987546'} {'name': 'Switchboard', 'number': '48621364'}
Now, I got dictionary FilteredData, which already contains some items from RawData: {'name': 'IT-support', 'number': '32136994'} {'name': 'Company Customer Service', 'number': '123987546'}
As you can see, Customer Service and Company Customer Service both have the same values, but different keys. In my project, there might be hundreds of similar duplicates, and we only want unique numbers to end up in FilteredData.
FilteredData is what we will be using later in the code, and RawData will be discarded.
Their names(keys) can be close duplicates, but not their numbers(values)**
There are two ways to do this.
A. Remove the duplicate items in RawData, before appending them into FilteredData.
B. Append them into FilteredData, and go through the numbers(values) there, removing the duplicates. Can I use a set here to do that? It would work on a list, obviously.
I'm not looking for the most time-efficient solution. I'd like the most simple and easy to learn one, if and when someone takes over my job someday. In my project it's mandatory for the next guy working on the code to get a quick grip of it.
I've already looked at sets, and tried to face the problem by nesting two for loops, but something tells me there gotta be an easier way.
Of course I might have missed the obvious solution here.
Thanks in advance!

I hope I understands your problem here:
data = [{'name': 'Customer Service', 'number': '123987546'}, {'name': 'Switchboard', 'number': '48621364'}]
newdata = [{'name': 'IT-support', 'number': '32136994'}, {'name': 'Company Customer Service', 'number': '123987546'}]
def main():
numbers = set()
for entry in data:
numbers.add(entry['number'])
for entry in newdata:
if entry['number'] not in numbers:
data.append(entry)
print data
main()
Output:
[{'name': 'Customer Service', 'number': '123987546'},
{'name': 'Switchboard', 'number': '48621364'},
{'name': 'IT-support', 'number': '32136994'}]

What you can do is take a dict.values(), create a set of those to remove duplicates and then go through the old dictionary and find the first key with that value and add it to a new one. Keep the set around because when you get the next dict entry, try adding the element to that set and see if the length of the set is longer that before adding it. If it is, it's a unique element and you can add it to the dict.

If you're willing on changing how FilteredData is currently, you can just use a dict and use the number as your key:
RawData = [
{'name': 'Customer Service', 'number': '123987546'},
{'name': 'Switchboard', 'number': '48621364'}
]
# Change how FilteredData is structured
FilteredDataMap = {
'32136994':
{'name': 'IT-support', 'number': '32136994'},
'123987546':
{'name': 'Company Customer Service', 'number': '123987546'}
}
for item in RawData:
number = item.get('number')
if number not in FilteredDataMap:
FilteredDataMap[number] = item
# If you need the list of items
FilteredData = list(FilteredDataMap.values())
You can just pull the actual list from the Map using .values()

I take the numbers are unique. Then, another solution would be taking advantage of the uniqueness of dictionary keys. This means converting each list of dictionary to a dictionary of 'number:name' pairs. Then, you simple need to update RawData with FilteredData.
RawData = [
{'name': 'Customer Service', 'number': '123987546'},
{'name': 'Switchboard', 'number': '48621364'}
]
FilteredData = [
{'name': 'IT-support', 'number': '32136994'},
{'name': 'Company Customer Service', 'number': '123987546'}
]
def convert_list(input_list):
return {item['number']:item['name'] for item in input_list}
def unconvert_dict(input_dict):
return [{'name':val, 'number': key} for key, val in input_dict.items()]
NewRawData = convert_list(RawData)
NewFilteredData = conver_list(FilteredData)
DesiredResultConverted = NewRawData.update(NewFilteredData)
DesuredResult = unconvert_dict(DesiredResultConverted)
In this example, the variables will have the following values:
NewRawData = {'123987546':'Customer Service', '48621364': 'Switchboard'}
NewFilteredData = {'32136994': 'IT-support', '123987546': 'Company Customer Service'}
When you update NewRawData with NewFilteredData, Company Customer Service will overwrite Customer Service as the value associated with the key 123987546. So,
DesiredResultConverted = {'123987546':'Company Customer Service', '48621364': 'Switchboard', '32136994': 'IT-support'}
Then, if you still prefer the original format, you can "unconvert" back.

Use list of indices to manipulate a nested dictionary

I'm trying to perform operations on a nested dictionary (data retrieved from a yaml file):
data = {'services': {'web': {'name': 'x'}}, 'networks': {'prod': 'value'}}
I'm trying to modify the above using the inputs like:
{'services.web.name': 'new'}
I converted the above to a list of indices ['services', 'web', 'name']. But I'm not able to/not sure how to perform the below operation in a loop:
data['services']['web']['name'] = new
That way I can modify dict the data. There are other values I plan to change in the above dictionary (it is extensive one) so I need a solution that works in cases where I have to change, EG:
data['services2']['web2']['networks']['local'].
Is there a easy way to do this? Any help is appreciated.

You may iterate over the keys while moving a reference:
data = {'networks': {'prod': 'value'}, 'services': {'web': {'name': 'x'}}}
modification = {'services.web.name': 'new'}
for key, value in modification.items():
keyparts = key.split('.')
to_modify = data
for keypart in keyparts[:-1]:
to_modify = to_modify[keypart]
to_modify[keyparts[-1]] = value
print(data)
Giving:
{'networks': {'prod': 'value'}, 'services': {'web': {'name': 'new'}}}