## Python: Using a List of Lists in a Function

n = [[1, 2, 3], [4, 5, 6, 7, 8, 9]]
def flatten(lists):
results = []
for lst in lists:
for numbers in lst:
results.append(numbers)
return results
print flatten(n)
WordPress keeps trying to remove my indentations, which is a pretty huge problem. Lines 3 and 4 should be more indented than 1 an 2. Line 5 has an additional indentation and line 6 has one more . Line 7 is less indented by 2 and line 8 returns to the original level of indendation.

## Python: How to Merge/Join 2 Lists

m = [1, 2, 3]
n = [4, 5, 6]

def join_lists(x, y):
return x+y

print join_lists(m, n)
# You want this to print [1, 2, 3, 4, 5, 6]

## Python: use ”.join(list) to concatenate a list of strings

n = [“Michael”, “Lieberman”]
def join_strings(words):
result = “”
for  i in words:
result = ”.join(words)
print result
return result

‘ ‘.join(list) if you want spaces

## Python: List appends and other list functions

list.append(x)
Add an item to the end of the list; equivalent to a[len(a):] = [x].

list.extend(L)
Extend the list by appending all the items in the given list; equivalent to a[len(a):] = L.

list.insert(ix)
Insert an item at a given position. The first argument is the index of the element before which to insert, so a.insert(0, x) inserts at the front of the list, anda.insert(len(a), x) is equivalent to a.append(x).

list.remove(x)
Remove the first item from the list whose value is x. It is an error if there is no such item.

list.pop([i])
Remove the item at the given position in the list, and return it. If no index is specified, a.pop() removes and returns the last item in the list. (The square brackets around the i in the method signature denote that the parameter is optional, not that you should type square brackets at that position. You will see this notation frequently in the Python Library Reference.)

list.index(x)
Return the index in the list of the first item whose value is x. It is an error if there is no such item.

list.count(x)
Return the number of times x appears in the list.

list.sort()
Sort the items of the list, in place.

list.reverse()
Reverse the elements of the list, in place.

An example that uses most of the list methods:

>>>

`>>> a = [66.25, 333, 333, 1, 1234.5]>>> print a.count(333), a.count(66.25), a.count('x')2 1 0>>> a.insert(2, -1)>>> a.append(333)>>> a[66.25, 333, -1, 333, 1, 1234.5, 333]>>> a.index(333)1>>> a.remove(333)>>> a[66.25, -1, 333, 1, 1234.5, 333]>>> a.reverse()>>> a[333, 1234.5, 1, 333, -1, 66.25]>>> a.sort()>>> a[-1, 1, 66.25, 333, 333, 1234.5]`

## Python: Add each element of a list

n = [3, 5, 7]

def total(numbers):
result = 0
for i in range(len(numbers)):
for i in numbers:
result = sum(numbers)
print result
return result

## Python: Counting up the elements in a list of arbitrary size in a function

Now that we’ve learned about`range`, we have two ways of iterating through a list.

Method 1 – `for item in list`:

``````for item in list:
print item
``````

Method 2 – iterate through indexes:

``````for i in range(len(list)):
print list[i]
``````

Method 1 is a little easier, but can cause problems when trying to modify the list. Method 2 is much safer. Since we aren’t modifying the list, feel free to use either one on this lesson!

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