mylist = [1,2,3,4]
mylist.append(5) #works fine,

def adding(mylist):
    mylist.append(5)

print adding(mylist) #will print out the orginal list without the 5.

data2 = data3 = [1,2,3]
data2 = data2 +[4]+[5]+[6] # doesn't works
data3 += [4] +[5] +[6] #works

#include <stdio.h>

void adding(int i) {
    i = i + 1;
}

int main() {
    int i = 0;
    adding(i);
    printf("i is %dn", i);  // will print "i is 0"
    return 0;
}

#include <iostream>

void adding(int &i) {
    i = i + 1;
}

int main() {
    int i = 0;
    adding(i);
    std::cout << "i is " << i << std::endl;  // will print "i is 1"
    return 0;
}

# Case 1
mylist = [1,2,3,4]
mylist.append(5)  # will print [1,2,3,4,5]

# Case 2
mylist = [1,2,3,4]
def adding(mylist):
    mylist.append(5)

adding(mylist)
print mylist  # will print [1,2,3,4,5]

# Case 3
mylist = [1,2,3,4]
def adding(mylist):
    mylist = mylist + [5]

adding(mylist)
print mylist  # will print [1,2,3,4]

# Case 4
mylist = [1,2,3,4]
def adding(mylist):
    mylist += [5]

adding(mylist)
print mylist  # will print [1,2,3,4,5]

def adding(mylist):
    mylist.append(5)

print adding(mylist)

def adding(mylist):
    mylist.append(5)
    return mylist
print adding(mylist)

adding(mylist)
print mylist

>>> data2 = data3 = [4, 5, 6]
>>> data2 = data2 + [1] + [2] + [3]
>>> print data2
[4, 5, 6, 1, 2, 3]
>>> data3 += [1] + [2] + [3]
>>> print data3
[4, 5, 6, 1, 2, 3]

def adding(mylist):
    mylist.append(5)

test_list = range(5)

print adding(test_list)

print test_list

adding(test_list)

print test_list

None
[0, 1, 2, 3, 4, 5]
[0, 1, 2, 3, 4, 5, 5]

def adding(mylist):
    mylist.append(5)

print adding(mylist)

print mylist
[1,2,3,4,5]

data2 = data3 = [1,2,3]
data2 = data2 +[4]+[5]+[6] #Actually works