Add missing syntax highlighting to python.md (#2154)

Fixes missing code highlighting in half of the Python code snippets.

The top half of the page had code examples formatted as code blocks with
4 space character indentations and no syntax highlighting as a result.

The bottom half on the other hand, used code blocks surrounded by
"```py" formatting brackets which hints to many markdown renders that
syntax highlighting should be applied.

This unifies the code blocks in the top half of the page to use the same
formatting syntax used in the bottom half with syntax highlighting.

This change was prompted by requests to add the syntax highlighting in
comments on the https://devhints.io/python page.

python.md

@@ -5,121 +5,138 @@ category: Python
 
 ### Tuples (immutable)
 
-    tuple = ()
+```py
+tuple = ()
+```
 
 ### Lists (mutable)
 
-    list = []
-    list[i:j]  # returns list subset
-    list[-1]   # returns last element
-    list[:-1]  # returns all but the last element
-    *list      # expands all elements in place
-
-    list[i] = val
-    list[i:j] = otherlist  # replace ith to jth-1 elements with otherlist
-    del list[i:j]
-
-    list.append(item)
-    list.extend(another_list)
-    list.insert(index, item)
-    list.pop()        # returns and removes last element from the list
-    list.pop(i)       # returns and removes i-th element from the list
-    list.remove(i)    # removes the first item from the list whose value is i
-    list1 + list2     # combine two list    
-    set(list)         # remove duplicate elements from a list
-
-    list.reverse()    # reverses the elements of the list in-place
-    list.count(item)
-    sum(list)
-
-    zip(list1, list2)  # returns list of tuples with n-th element of both list1 and list2
-    list.sort()        # sorts in-place, returns None
-    sorted(list)       # returns sorted copy of list
-    ",".join(list)     # returns a string with list elements seperated by comma
+```py
+list = []
+list[i:j]  # returns list subset
+list[-1]   # returns last element
+list[:-1]  # returns all but the last element
+*list      # expands all elements in place
+
+list[i] = val
+list[i:j] = otherlist  # replace ith to jth-1 elements with otherlist
+del list[i:j]
+
+list.append(item)
+list.extend(another_list)
+list.insert(index, item)
+list.pop()        # returns and removes last element from the list
+list.pop(i)       # returns and removes i-th element from the list
+list.remove(i)    # removes the first item from the list whose value is i
+list1 + list2     # combine two list    
+set(list)         # remove duplicate elements from a list
+
+list.reverse()    # reverses the elements of the list in-place
+list.count(item)
+sum(list)
+
+zip(list1, list2)  # returns list of tuples with n-th element of both list1 and list2
+list.sort()        # sorts in-place, returns None
+sorted(list)       # returns sorted copy of list
+",".join(list)     # returns a string with list elements separated by comma
+
+```
 
 ### Dict
 
-    dict = {}
-    dict.keys()
-    dict.values()
-    "key" in dict    # let's say this returns False, then...
-    dict["key"]      # ...this raises KeyError
-    dict.get("key")  # ...this returns None
-    dict.setdefault("key", 1)
-    **dict           # expands all k/v pairs in place
+```py
+dict = {}
+dict.keys()
+dict.values()
+"key" in dict    # let's say this returns False, then...
+dict["key"]      # ...this raises KeyError
+dict.get("key")  # ...this returns None
+dict.setdefault("key", 1)
+**dict           # expands all k/v pairs in place
+```
 
 ### Iteration
 
-    for item in ["a", "b", "c"]:
-    for i in range(4):        # 0 to 3
-    for i in range(4, 8):     # 4 to 7
-    for i in range(1, 9, 2):  # 1, 3, 5, 7
-    for key, val in dict.items():
-    for index, item in enumerate(list):
+```py
+for item in ["a", "b", "c"]:
+for i in range(4):        # 0 to 3
+for i in range(4, 8):     # 4 to 7
+for i in range(1, 9, 2):  # 1, 3, 5, 7
+for key, val in dict.items():
+for index, item in enumerate(list):
+```
 
 ### [String](https://docs.python.org/2/library/stdtypes.html#string-methods)
 
-    str[0:4]
-    len(str)
-
-    string.replace("-", " ")
-    ",".join(list)
-    "hi {0}".format('j')
-    f"hi {name}" # same as "hi {}".format('name')
-    str.find(",")
-    str.index(",")   # same, but raises IndexError
-    str.count(",")
-    str.split(",")
-
-    str.lower()
-    str.upper()
-    str.title()
-
-    str.lstrip()
-    str.rstrip()
-    str.strip()
-
-    str.islower()
-
-    /* escape characters */
-    >>> 'doesn\'t'  # use \' to escape the single quote...
-        "doesn't"
-    >>> "doesn't"  # ...or use double quotes instead
-        "doesn't"
-    >>> '"Yes," they said.'
-        '"Yes," they said.'
-    >>> "\"Yes,\" they said."
-        '"Yes," they said.'
-    >>> '"Isn\'t," they said.'
-        '"Isn\'t," they said.'
+```py
+str[0:4]
+len(str)
+
+string.replace("-", " ")
+",".join(list)
+"hi {0}".format('j')
+f"hi {name}" # same as "hi {}".format('name')
+str.find(",")
+str.index(",")   # same, but raises IndexError
+str.count(",")
+str.split(",")
+
+str.lower()
+str.upper()
+str.title()
+
+str.lstrip()
+str.rstrip()
+str.strip()
+
+str.islower()
+
+/* escape characters */
+>>> 'doesn\'t'  # use \' to escape the single quote...
+    "doesn't"
+>>> "doesn't"  # ...or use double quotes instead
+    "doesn't"
+>>> '"Yes," they said.'
+    '"Yes," they said.'
+>>> "\"Yes,\" they said."
+    '"Yes," they said.'
+>>> '"Isn\'t," they said.'
+    '"Isn\'t," they said.'
+```
 
 ### Casting
 
-    int(str)
-    float(str)
-    str(int)
-    str(float)
-    'string'.encode()
+```py
+int(str)
+float(str)
+str(int)
+str(float)
+'string'.encode()
+```
 
 ### Comprehensions
 
-    [fn(i) for i in list]            # .map
-    map(fn, list)                    # .map, returns iterator
-
-    filter(fn, list)                 # .filter, returns iterator
-    [fn(i) for i in list if i > 0]   # .filter.map
+```py
+[fn(i) for i in list]            # .map
+map(fn, list)                    # .map, returns iterator
+
+filter(fn, list)                 # .filter, returns iterator
+[fn(i) for i in list if i > 0]   # .filter.map
+```
 
 ### Regex
 
-    import re
+```py
+import re
 
-    re.match(r'^[aeiou]', str)
-    re.sub(r'^[aeiou]', '?', str)
-    re.sub(r'(xyz)', r'\1', str)
+re.match(r'^[aeiou]', str)
+re.sub(r'^[aeiou]', '?', str)
+re.sub(r'(xyz)', r'\1', str)
 
-    expr = re.compile(r'^...$')
-    expr.match(...)
-    expr.sub(...)
+expr = re.compile(r'^...$')
+expr.match(...)
+expr.sub(...)
+```
 
 ## File manipulation