Python Forum

I am new to python and programming in general.I wanted to write a code which prints the similar elements from 2 lists .For example if a=[1,2,3,4,5] and b=[0,2,4,6] , I would want a c=[2,4]. Here is what I did:

def simi(a,b):
    a,b,c=[],[],[]
    for i in a:
        for j in b:
            if i==j:
                c.append(i)
            else:
                continue
    return (c)

[python]

check your line#2
Do you really want to overwrite the user supplied arguments a and b with empty lists? :-)

Note that your code is not pythonic and there are better ways to do the same, without using nested loops. check using set

(Jun-22-2018, 06:57 AM)DRPR Wrote: [ -> ]I am new to python and programming in general.I wanted to write a code which prints the similar elements from 2 lists .For example if a=[1,2,3,4,5] and b=[0,2,4,6] , I would want a c=[2,4]. Here is what I did:

def simi(a,b):
    a,b,c=[],[],[]
    for i in a:
        for j in b:
            if i==j:
                c.append(i)
            else:
                continue
    return (c)

• In your function, you overwrite a and b, you have to initialize only c
  
• If you find an equal element - you can stop the search
  

             if i==j:
                 c.append(i)
                 break

• You don't need else for an empty action - if may exist without else. You only use continue if you have more code in the loop that you want to bypass - and even then it is not advised (unless you want to avoid indenting large block of code)
  
• It is more efficient to check the presence of an element in a list with an operator in
  
• One-letter names are bad practice (with very few exceptions). Variable names are a part of the code documentation, and should tell the code reader their purpose. It is advisable to acquire the habit of naming your variables properly early in the study process
  

So this is how your function should look like

def similar_elements(list1, list2):
    similars = []
    for elem in list1:
        if elem in list2:
            similars.append(elem)
    return similars

Of course, experienced Pythonista would write it at least as

[elem for elem in list1 if elem in list2]

and there are couple of other ways to write it - but that will come in the future.

Good luck with your studies!

(Jun-22-2018, 07:29 AM)volcano63 Wrote: [ -> ][quote='DRPR' pid='50443' dateline='1529650625'] I am new to python and programming in general.I wanted to write a code which prints the similar elements from 2 lists .For example if a=[1,2,3,4,5] and b=[0,2,4,6] , I would want a c=[2,4]. Of course, experienced Pythonista would write it at least as

[elem for elem in list1 if elem in list2]

and there are couple of other ways to write it - but that will come in the future. Good luck with your studies!

I did the method for the experienced pythonista! but it returned a an error:

def simi1(list1,list2):
    c=[]
    [elem for elem in list1 if elem in list2]
    c.append(elem)
    return(c)

Error:
NameError: name 'elem' is not defined

Any tips?

(Jun-22-2018, 09:55 AM)DRPR Wrote: [ -> ]I did the method for the experienced pythonista! but it returned a an error:

def simi1(list1,list2):
    c=[]
    [elem for elem in list1 if elem in list2]
    c.append(elem)
    return(c)

Error:
NameError: name 'elem' is not defined

Any tips?

I probably should not have shown it (if I hadn't, someone had probably "corrected" me ). I have committed a sin I often berate others for - showing an advanced technique to a newbie without a disclaimer.

This is the proper code

def simi1(list1,list2):
    return [elem for elem in list1 if elem in list2]

or - by set, as buran suggested

def simi1(list1,list2):
    return set(list1).intersection(list2)

The problem with those 2 solutions for you - jumping stages. Mastering loops is a step to mastering list comprehension.