General¶
join method: Turn an Iterable into a Python String¶
If you want to turn an iterable into a string, use join().
In the code below, I join elements in the list fruits using “, “.
fruits = ['apples', 'oranges', 'grapes']
fruits_str = ', '.join(fruits)
print(f"Today, I need to get some {fruits_str} in the grocery store")
Today, I need to get some apples, oranges, grapes in the grocery store
Zip: Associate Elements from Two Iterators based on the Order¶
If you want to associate elements from two iterators based on the order, combine list and zip.
nums = [1, 2, 3, 4]
string = "abcd"
combinations = list(zip(nums, string))
for comb in combinations:
print(comb)
(1, 'a')
(2, 'b')
(3, 'c')
(4, 'd')
Zip Function: Create Pairs of Elements from Two Lists in Python¶
If you want to create pairs of elements from two lists, use zip. zip() function takes iterables and aggregates them in a tuple.
You can also unzip the list of tuples by using zip(*list_of_tuples).
nums = [1, 2, 3, 4]
chars = ['a', 'b', 'c', 'd']
comb = list(zip(nums, chars))
comb
[(1, 'a'), (2, 'b'), (3, 'c'), (4, 'd')]
nums_2, chars_2 = zip(*comb)
nums_2, chars_2
((1, 2, 3, 4), ('a', 'b', 'c', 'd'))
Stop using = operator to create a copy of a Python list. Use copy method instead¶
When you create a copy of a Python list using the = operator, a change in the new list will lead to the change in the old list. It is because both lists point to the same object.
l1 = [1, 2, 3]
l2 = l1
l2.append(4)
l2
[1, 2, 3, 4]
l1
[1, 2, 3, 4]
Instead of using = operator, use copy() method. Now your old list will not change when you change your new list.
l1 = [1, 2, 3]
l2 = l1.copy()
l2.append(4)
l2
[1, 2, 3, 4]
l1
[1, 2, 3]
Enumerate: Get Counter and Value While Looping¶
Are you using for i in range(len(array)) to access both the index and the value of the array? If so, use enumerate instead. It produces the same result but it is much cleaner.
arr = ['a', 'b', 'c', 'd', 'e']
# Instead of this
for i in range(len(arr)):
print(i, arr[i])
0 a
1 b
2 c
3 d
4 e
# Use this
for i, val in enumerate(arr):
print(i, val)
0 a
1 b
2 c
3 d
4 e
set.intersection: Find the Intersection Between 2 Sets¶
If you want to get the common elements between 2 lists, convert lists to sets then use set.intersection to find the intersection between 2 sets.
requirement1 = ['pandas', 'numpy', 'statsmodel']
requirement2 = ['numpy', 'statsmodel', 'sympy', 'matplotlib']
intersection = set.intersection(set(requirement1), set(requirement2))
list(intersection)
['statsmodel', 'numpy']
Set Difference: Find the Difference Between 2 Sets¶
If you want to find the difference between 2 lists, turn those lists into sets then apply the difference() method to the sets.
a = [1, 2, 3, 4]
b = [1, 3, 4, 5, 6]
# Find elements in a but not in b
diff = set(a).difference(set(b))
print(list(diff))
[2]
# Find elements in b but not in a
diff = set(b).difference(set(a))
print(list(diff)) # [5, 6]
[5, 6]
Difference between list append and list extend¶
If you want to add a list to another list, use the append method. To add elements of a list to another list, use the extend method.
# Add a list to a list
a = [1, 2, 3, 4]
a.append([5, 6])
a
[1, 2, 3, 4, [5, 6]]
a = [1, 2, 3, 4]
a.extend([5, 6])
a
[1, 2, 3, 4, 5, 6]