diff --git a/python/builtins.py b/python/builtins.py
index 4abb8187..9528160b 100644
--- a/python/builtins.py
+++ b/python/builtins.py
@@ -96,14 +96,129 @@ def sorted(iterable, reverse=False, key=None):
     return a
 
 ##### str #####
-def __f(self, *args):
-    if '{}' in self:
-        for i in range(len(args)):
-            self = self.replace('{}', str(args[i]), 1)
-    else:
-        for i in range(len(args)):
-            self = self.replace('{'+str(i)+'}', str(args[i]))
-    return self
+def __f(self:str, *args, **kwargs) -> str:
+    def tokenizeString(s:str):
+        tokens = []
+        L, R = 0,0
+        
+        mode = None
+        curArg = 0
+        # lookingForKword = False
+        
+        while(R<len(s)):
+            curChar = s[R]
+            nextChar = s[R+1] if R+1<len(s) else ''
+            
+            # Invalid case 1: stray '}' encountered, example: "ABCD EFGH {name} IJKL}", "Hello {vv}}", "HELLO {0} WORLD}"
+            if curChar == '}' and nextChar != '}':
+                raise ValueError("Single '}' encountered in format string")        
+            
+            # Valid Case 1: Escaping case, we escape "{{ or "}}" to be "{" or "}", example: "{{}}", "{{My Name is {0}}}"
+            if (curChar == '{' and nextChar == '{') or (curChar == '}' and nextChar == '}'):
+                
+                if (L<R): # Valid Case 1.1: make sure we are not adding empty string
+                    tokens.append(s[L:R]) # add the string before the escape
+                
+                
+                tokens.append(curChar) # Valid Case 1.2: add the escape char
+                L = R+2 # move the left pointer to the next char
+                R = R+2 # move the right pointer to the next char
+                continue
+            
+            # Valid Case 2: Regular command line arg case: example:  "ABCD EFGH {} IJKL", "{}", "HELLO {} WORLD"
+            elif curChar == '{' and nextChar == '}':
+                if mode is not None and mode != 'auto':
+                    # Invalid case 2: mixing automatic and manual field specifications -- example: "ABCD EFGH {name} IJKL {}", "Hello {vv} {}", "HELLO {0} WORLD {}" 
+                    raise ValueError("Cannot switch from manual field numbering to automatic field specification")
+                
+                mode = 'auto'
+                if(L<R): # Valid Case 2.1: make sure we are not adding empty string
+                    tokens.append(s[L:R]) # add the string before the special marker for the arg
+                
+                tokens.append("{"+str(curArg)+"}") # Valid Case 2.2: add the special marker for the arg
+                curArg+=1 # increment the arg position, this will be used for referencing the arg later
+                
+                L = R+2 # move the left pointer to the next char
+                R = R+2 # move the right pointer to the next char
+                continue
+            
+            # Valid Case 3: Key-word arg case: example: "ABCD EFGH {name} IJKL", "Hello {vv}", "HELLO {name} WORLD"
+            elif (curChar == '{'):
+                
+                if mode is not None and mode != 'manual':
+                    # # Invalid case 2: mixing automatic and manual field specifications -- example: "ABCD EFGH {} IJKL {name}", "Hello {} {1}", "HELLO {} WORLD {name}"
+                    raise ValueError("Cannot switch from automatic field specification to manual field numbering")
+                
+                mode = 'manual'
+                
+                if(L<R): # Valid case 3.1: make sure we are not adding empty string
+                    tokens.append(s[L:R]) # add the string before the special marker for the arg
+                
+                # We look for the end of the keyword          
+                kwL = R # Keyword left pointer
+                kwR = R+1 # Keyword right pointer
+                while(kwR<len(s) and s[kwR]!='}'):
+                    if s[kwR] == '{': # Invalid case 3: stray '{' encountered, example: "ABCD EFGH {n{ame} IJKL {", "Hello {vv{}}", "HELLO {0} WOR{LD}"
+                        raise ValueError("Unexpected '{' in field name")
+                    kwR += 1
+                
+                # Valid case 3.2: We have successfully found the end of the keyword
+                if kwR<len(s) and s[kwR] == '}':
+                    tokens.append(s[kwL:kwR+1]) # add the special marker for the arg
+                    L = kwR+1
+                    R = kwR+1
+                    
+                # Invalid case 4: We didn't find the end of the keyword, throw error
+                else:
+                    raise ValueError("Expected '}' before end of string")
+                continue
+            
+            R = R+1
+        
+        
+        # Valid case 4: We have reached the end of the string, add the remaining string to the tokens 
+        if L<R:
+            tokens.append(s[L:R])
+                
+        # print(tokens)
+        return tokens
+
+    tokens = tokenizeString(self)
+    argMap = {}
+    for i, a in enumerate(args):
+        argMap[str(i)] = a
+    final_tokens = []
+    for t in tokens:
+        if t[0] == '{' and t[-1] == '}':
+            key = t[1:-1]
+            argMapVal = argMap.get(key, None)
+            kwargsVal = kwargs.get(key, None)
+                                    
+            if argMapVal is None and kwargsVal is None:
+                raise ValueError("No arg found for token: "+t)
+            elif argMapVal is not None:
+                final_tokens.append(str(argMapVal))
+            else:
+                final_tokens.append(str(kwargsVal))
+        else:
+            final_tokens.append(t)
+    
+    return ''.join(final_tokens)
+
+    # if '{}' in self:
+    #     for i in range(len(args)):
+    #         self = self.replace('{}', str(args[i]), 1)
+    # else:
+    #     # Positional arguments will be followed by keyword arguments
+    #     # 1. Replace the positional arguments
+    #     for i,a in enumerate(args):
+    #         self = self.replace('{'+str(i)+'}', str(a))
+        
+    #     # 2. Replace the keyword arguments
+    #     for k,v in kwargs.items():
+    #         self = self.replace('{'+k+'}', str(v))
+    
+    # return self
 str.format = __f
 
 def __f(self, chars=None):