function for extracting data from lists

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function for extracting data from lists - Paulman - Nov-08-2021

Hi,
I'm struggling with this problem:
create a function named get_data, that takes two arguments, Data and Key.
- Data is the list of dictionaries in list_1
- Key are the data that I need to extract from the list of dictionaries list_1.
This function should then return a list of these attributes.

Example 1:
Input:
get_data(list_1, “name”)
Output:
[“Jerome","Ibraheem","Tiana","Lucas","Rickie”]

Example 2:
Input:
get_data(list_1, “weight”)
Output:
[3.38,3.08,0.81,3.33,4.4]

I did the following code, but I get as output only the first line:

def main(list_1):
    return main

list_1 = [
               {'name': 'Jerome', 'weight': 3.38, 'wingspan': 49.96, 'length': 19.75},
               {'name': 'Ibraheem', 'weight': 3.08, 'wingspan': 50.59, 'length': 20.6},
               {'name': 'Tiana', 'weight': 0.81, 'wingspan': 47.86, 'length': 17.94},
               {'name': 'Lucas', 'weight': 3.33, 'wingspan': 48.27, 'length': 18.77},
               {'name': 'Rickie', 'weight': 4.4, 'wingspan': 51.0, 'length': 20.34}
                ]

def get_data(data,key):
    for key in data:
        return key
data = list_1
key = []
output = get_data(data,key)
print(output)

What do I assign to "key" to get the correct output?

RE: function for extracting data from lists - Larz60+ - Nov-08-2021

You need to iterate through the list, check if key in in the dictionary, and if so display results

pseudo code:

for each item in list_1
    for each key in keys
        display key and value (no newline)
    display newline

to display without newline, use like: print(f"{key:8} {adict[key]:10} ", end="")
the :8 and :10 are qualifiers that indicate width of field.

RE: function for extracting data from lists - Paulman - Nov-08-2021

OK thanks, then I did the following code:

def main(list_1):
    return main

list_1 = [
    {'name': 'Jerome', 'weight': 3.38, 'wingspan': 49.96, 'length': 19.75},
    {'name': 'Ibraheem', 'weight': 3.08, 'wingspan': 50.59, 'length': 20.6},
    {'name': 'Tiana', 'weight': 0.81, 'wingspan': 47.86, 'length': 17.94},
    {'name': 'Lucas', 'weight': 3.33, 'wingspan': 48.27, 'length': 18.77},
    {'name': 'Rickie', 'weight': 4.4, 'wingspan': 51.0, 'length': 20.34}
]

def get_data(data,key):
    y=[]
    for x in data:
        return y=x[key]
data = list_1
get_data(list_1,'length')
output = get_data(data,key)
print(output, end=" ")

I'm getting a syntax error in "return y=x[key]", why is that?

RE: function for extracting data from lists - ndc85430 - Nov-09-2021

Why are you trying to assign to a variable in a return statement? return is for returning a value to the caller of the function.

RE: function for extracting data from lists - Paulman - Nov-09-2021

OK thanks, then my understanding from your comment is the below, but didn't work as well:

def main(list_1):
    return main
 
list_1 = [
    {'name': 'Jerome', 'weight': 3.38, 'wingspan': 49.96, 'length': 19.75},
    {'name': 'Ibraheem', 'weight': 3.08, 'wingspan': 50.59, 'length': 20.6},
    {'name': 'Tiana', 'weight': 0.81, 'wingspan': 47.86, 'length': 17.94},
    {'name': 'Lucas', 'weight': 3.33, 'wingspan': 48.27, 'length': 18.77},
    {'name': 'Rickie', 'weight': 4.4, 'wingspan': 51.0, 'length': 20.34}
]
 
def get_data(data,key):
    y = []
    for x in data:
      y=x[key]
      return y
data = list_1
get_data(list_1,'length')
output = get_data(data,key)
print(output, end=" ")

RE: function for extracting data from lists - Larz60+ - Nov-09-2021

Try:

list_1 = [
    {'name': 'Jerome', 'weight': 3.38, 'wingspan': 49.96, 'length': 19.75},
    {'name': 'Ibraheem', 'weight': 3.08, 'wingspan': 50.59, 'length': 20.6},
    {'name': 'Tiana', 'weight': 0.81, 'wingspan': 47.86, 'length': 17.94},
    {'name': 'Lucas', 'weight': 3.33, 'wingspan': 48.27, 'length': 18.77},
    {'name': 'Rickie', 'weight': 4.4, 'wingspan': 51.0, 'length': 20.34}
]

def get_data(data, keys):
    for adict in list_1:
        for key in keys:
            if key in adict:
                print(f"{key:8} {adict[key]:10} ", end="")
        print()

def testit():
    get_data(["Jerome","Ibraheem","Tiana","Lucas","Rickie"], ['name', 'weight'])

testit()

gives you:

Output:name     Jerome     weight         3.38 
name     Ibraheem   weight         3.08 
name     Tiana      weight         0.81 
name     Lucas      weight         3.33 
name     Rickie     weight          4.4

RE: function for extracting data from lists - ibreeden - Nov-09-2021

(Sorry Larz, we were almost at the same time answering.)

Very well, you are making progress. But you should be more precise than saying: " but didn't work as well". You get the following message, right?

Error:Traceback (most recent call last):
  File "/home/ibreeden/PycharmProjects/Forum/venv/impos01.py", line 23, in <module>
    output = get_data(data, key)
NameError: name 'key' is not defined

It is because you write:

get_data(list_1,'length')
output = get_data(data,key)

Replace that with:

output = get_data(list_1, 'length')

Output:
19.75

Now this is still not what you want, because this is only the first occurence.
In the function get_data() you have a return in the for-loop. That is wrong. You must return after the loop has finished. So unindent the return statement.

Output:
20.34

Still not what you want, now it shows only the last occurrence. Have a look at the list "y = []". Do you know how to append() values to a list?

RE: function for extracting data from lists - Paulman - Nov-09-2021

Thanks for the help, I'm nearly there.... hopefully: now I have the code below that works and gives the last value of the list as you said. Then I tried to use "append" in order to have all the values (or names) and from my understanding I should append the output of each iteration inside the loop, but still get error "'float' object has no attribute 'append'", as per the below code. So how can I append each output from the for loop to the previous one in order to get the desired results in one line, e.g. [19.75, 20.06, 17.94, 18.77, 20.34]?

def main(list_1):
    return main
  
list_1 = [
    {'name': 'Jerome', 'weight': 3.38, 'wingspan': 49.96, 'length': 19.75},
    {'name': 'Ibraheem', 'weight': 3.08, 'wingspan': 50.59, 'length': 20.6},
    {'name': 'Tiana', 'weight': 0.81, 'wingspan': 47.86, 'length': 17.94},
    {'name': 'Lucas', 'weight': 3.33, 'wingspan': 48.27, 'length': 18.77},
    {'name': 'Rickie', 'weight': 4.4, 'wingspan': 51.0, 'length': 20.34}
]
  
def get_data(data,key):
    y = []
    for x in data:
      y=x[key]
      y.append(x)
    return y
data = list_1
get_data(list_1,'length')
output = get_data(list_1, 'length')
print(output, end=" ")

RE: function for extracting data from lists - ibreeden - Nov-09-2021

Nono, this is what you do:

y = []       # create empty list with name "y"
...
y=x[key]     # y = 19.75; Now y is a floating point number
y.append(x)  # append something to a float???

append() is a method of list. So you must do:

y = []
...
y.append(x[key])

... and after the for-loop has finished you will have a list with all the data that you want.

RE: function for extracting data from lists - Paulman - Nov-09-2021

Wow... OK now I understand!! Many thanks, I was becoming crazy complicating thing and looping my brain instead of coding, now it finally works as expected (below the correct code). Many thanks again, in particular with the details: they helped me to understand things more linearly.

def main(list_1):
    return main
  
list_1 = [
    {'name': 'Jerome', 'weight': 3.38, 'wingspan': 49.96, 'length': 19.75},
    {'name': 'Ibraheem', 'weight': 3.08, 'wingspan': 50.59, 'length': 20.6},
    {'name': 'Tiana', 'weight': 0.81, 'wingspan': 47.86, 'length': 17.94},
    {'name': 'Lucas', 'weight': 3.33, 'wingspan': 48.27, 'length': 18.77},
    {'name': 'Rickie', 'weight': 4.4, 'wingspan': 51.0, 'length': 20.34}
]
  
def get_data(data,key):
    y = []
    for x in data:
      y.append(x[key])
    return y
data = list_1
get_data(list_1,'length')
output = get_data(list_1, 'length')
print(output, end=" ")