diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 565f60ef4..df049882b 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -39,7 +39,7 @@ Here's what you can do to help:
 - You can start creating a new snippet, by using the [snippet template](snippet_template.md) to format your snippets.
 - Updating the README.md file should only be done by altering the scripts in the **scripts** folder or altering their relative static parts in the **static-parts** folder.
 - You may tag your snippet in tag_databse although it is _not_ necessary.
-- You may add your name as `[Name][@github_username]` to the contributor database. If the snippet already exists and you are making changes to it you can add your name at the laste seperated by a comma.
+- You may add your name as `[Name][@github_username]` to the contributor database. If the snippet already exists and you are making changes to it you can add your name at the last seperated by a comma.
 <!--
 ### Additional guidelines and conventions regarding snippets
 
diff --git a/contributor_database b/contributor_database
index 66bbf0288..ff2c8420e 100644
--- a/contributor_database
+++ b/contributor_database
@@ -12,7 +12,7 @@ max_n:[Rohit Tanwar](@kriadmin)
 min_n:[Rohit Tanwar](@kriadmin)
 shuffle:[Rohit Tanwar](@kriadmin)
 spread:[Rohit Tanwar](@kriadmin)
-zip:[Rohit Tanwar](@kriadmin)
+zip:[Rohit Tanwar](@kriadmin),[Leonardo Galdino](@LeonardoGaldino)
 byte_size:[Rohit Tanwar](@kriadmin)
 capitalize:[Rohit Tanwar](@kriadmin)
 capitalize_every_word:[Rohit Tanwar](@kriadmin)
@@ -25,6 +25,6 @@ insertion_sort:[Meet Zaveri](@meetzaveri),[Rohit Tanwar](@kriadmin)
 difference_by:[Rohit Tanwar](@kriadmin)
 bubble_sort: [Shobhit Sachan](@sachans)
 has_duplicates: [Rob-Rychs](@Rob-Rychs)
-keys_only: [Rob-Rychs](@Rob-Rychs)
+keys_only: [Rob-Rychs](@Rob-Rychs),[Matteo Veraldi](@mattveraldi)
 values_only: [Rob-Rychs](@Rob-Rychs)
 all_unique: [Rob-Rychs](@Rob-Rychs)
\ No newline at end of file
diff --git a/snippets/byte_size.md b/snippets/byte_size.md
index faa8ba5fd..7f34b08df 100644
--- a/snippets/byte_size.md
+++ b/snippets/byte_size.md
@@ -2,7 +2,7 @@
 
 Returns the length of a string in bytes.
 
-`utf-8` encodes a given string and find its length.
+`utf-8` encodes a given string, then `len` finds the length of the encoded string.
 
 ```python
 def byte_size(string):
@@ -12,4 +12,4 @@ def byte_size(string):
 ```python
 byte_size('😀') # 4
 byte_size('Hello World') # 11
-```
\ No newline at end of file
+```
diff --git a/snippets/count_occurences.md b/snippets/count_occurences.md
index d6355d4df..7a3c930e7 100644
--- a/snippets/count_occurences.md
+++ b/snippets/count_occurences.md
@@ -2,7 +2,7 @@
 
 :information_source: Already implemented via `list.count()`.
 
-Counts the occurrences of a value in an list.
+Counts the occurrences of a value in a list.
 
 Uses the list comprehension to increment a counter each time you encounter the specific value inside the list.
 
diff --git a/snippets/count_vowels.md b/snippets/count_vowels.md
index 98b28ebf0..dc34acffe 100644
--- a/snippets/count_vowels.md
+++ b/snippets/count_vowels.md
@@ -7,12 +7,9 @@ Use a regular expression to count the number of vowels `(A, E, I, O, U)` in a st
 ```python
 import re
 
-
 def count_vowels(str):
     return len(re.findall(r'[aeiou]', str, re.IGNORECASE))
-```
 
-``` python
-count_vowels('foobar')  # 3
-count_vowels('gym')  # 0
+count_vowels('foobar') # 3
+count_vowels('gym')# 0
 ```
diff --git a/snippets/is_upper_case.md b/snippets/is_upper_case.md
index 5aa2a8287..6169cd424 100644
--- a/snippets/is_upper_case.md
+++ b/snippets/is_upper_case.md
@@ -11,6 +11,6 @@ def is_upper_case(string):
 
 ```python
 is_upper_case('ABC') # True
-is_upper_case('a3@$') # True
+is_upper_case('a3@$') # False
 is_upper_case('aB4') # False
-```
\ No newline at end of file
+```
diff --git a/snippets/keys_only.md b/snippets/keys_only.md
index f53a32107..7a566a1fd 100644
--- a/snippets/keys_only.md
+++ b/snippets/keys_only.md
@@ -2,14 +2,11 @@
 
 Function which accepts a dictionary of key value pairs and returns a new flat list of only the keys.
 
-Uses the .items() function with a for loop on the dictionary to track both the key and value and returns a new list by appending the keys to it. Best used on 1 level-deep key:value pair dictionaries (a flat dictionary) and not nested data-structures which are also commonly used with dictionaries. (a flat dictionary resembles a json and a flat list an array for javascript people).
+Uses the .keys() method of "dict" objects. dict.keys() returns a view object that displays a list of all the keys. Then, list(dict.keys()) returns a list that stores all the keys of a dict.
 
 ``` python
 def keys_only(flat_dict):
-    lst = []
-    for k, v in flat_dict.items():
-        lst.append(k)
-    return lst
+    return list(flat_dict.keys())
 ```
 
 ``` python
diff --git a/snippets/zip.md b/snippets/zip.md
index 2260bc926..bcb5567cd 100644
--- a/snippets/zip.md
+++ b/snippets/zip.md
@@ -12,7 +12,7 @@ def zip(*args, fillvalue=None):
     result = []
     for i in range(max_length):
         result.append([
-            args[k][i] if i < len(args[k]) else None for k in range(len(args))
+            args[k][i] if i < len(args[k]) else fillvalue for k in range(len(args))
         ])
     return result
 ```
diff --git a/test/keys_only/keys_only.py b/test/keys_only/keys_only.py
index 43d879917..ab1f21176 100644
--- a/test/keys_only/keys_only.py
+++ b/test/keys_only/keys_only.py
@@ -1,5 +1,2 @@
 def keys_only(flat_dict):
-    lst = []
-    for k, v in flat_dict.items():
-        lst.append(k)
-    return lst
\ No newline at end of file
+    return list(flat_dict.keys())
\ No newline at end of file