I need to perform below operations:

• iterate over a list of dictionary [{},{}]
  • call a transform function which transforms each dictionary, which returns a dictionary.
    • Here key and values are not static, but dataframe name and dataframe value. So dictionary may have one ore more key-value pair.
  • which I would need to store in a final dictionary

Expected : expected data would be a dictionary:

{"key1":"val1", "key2":"val2", "key3":"val3"} # ... in actual, the key would be dataframe name, value would be dataframe value

Simplified Use case:

dictname = [{"key1":"val1","key2":"val2"},{"key3":"value3"}] # input list of dictionary

def transform(each):
    return each # to oversimplify, this would be a dictionary with one or more keys with transformations.

final = {transform(each) for each in dictname}
final

went over other related threads on the issue, could not figure out as how to handle the specific case. Could anyone please guide?e

CodePudding user response：

There are several things wrong in your code.

The dict comprehension is as follows: {key: value, for key, value in something that outputs two things}. In your case transform_each outputs a dict. So fixing this we obtain:

dictname = {"key1":"val1","key2":"val2"} # input dictionary
def transform(each):
    return {each: "new_value"}
final = {key: transform(each) for key,  each in dictname.items()}
final  # {'key1': {'val1': 'new_value'}, 'key2': {'val2': 'new_value'}}

This is not what you want. You need to change only the value of the dict. That is the second thing wrong: Your function must output a value, not a dict. Otherwise, as seen, you got a dict of dicts. You can fix it as follows:

dictname = {"key1":"val1","key2":"val2"} # input dictionary

def transform(each):
    return "new_value"


final = {key: transform(each) for key,  each in dictname.items()}
final  # {'key1': 'new_value', 'key2': 'new_value'

CodePudding user response：

Define transform as

def transform(each):
    return <the new value>

and then use

result = {k: transform(k) for k in dictname}

If you cannot update transform use

from collections import ChainMap
result = dict(ChainMap(*(transform(k) for k in dictname)))

CodePudding user response：

This is an updated answer for the updated question. I think the following should do what you want:

dictname = [{"key1":"val1", "key2":"val2"}, {"key3":"val3"}]

def transform(each):
    return each

final = {k:v for d in dictname for k, v in transform(d).items()}

The transform function takes one of the dictionaries as an argument, and returns a dictionary. The returned dictionaries from all the calls to transform are combined into the top-level dictionary final.

The example above defined final to be:

{'key1': 'val1', 'key2': 'val2', 'key3': 'val3'}

In this example, transform merely returns the dict that was passed to it, but it could return any dict you want.