def myAppend$($str$,$ ch$)$: # Return a new string that is like str but with character ch added at the end return str $+$ ch def myCount$($str$,$ ch$)$: # Return the number of times character ch appears in str$.$ count $=0$ for char in str: if char $==$ ch: count $+=1$ return count def myExtend$($str$1,$ str$2)$: # Return a new string that contains the elements of str$1$ followed by the elements of str$2$ return str$1+$ str$2$ def myMin$($str$)$: # Return the character in str with the lowest ASCII code. if len$($str$)==0$: print$("$Empty string: no min value"$)$ return None min$\_$char $=$ str$[0]$ for char in str: if char $<$ min$\_$char: min$\_$char $=$ char return min$\_$char def myInsert$($str$,$ i$,$ ch$)$: # Return a new string like str except that ch has been inserted at the ith position. if i $>$ len$($str$)$: print$("$Invalid index"$)$ return None return str$[$:i$]+$ ch $+$ str$[$i:$]$ def myPop$($str$,$ i$)$: # Return two results: a new string with the ith element removed, and the value that was removed. if i $>=$ len$($str$)$: print$("$Invalid index"$)$ return str$,$ None removed$\_$char $=$ str$[$i$]$ new$\_$str $=$ str$[$:i$]+$ str$[$i$+1$:$]$ return new$\_$str$,$ removed$\_$char def myFind$($str$,$ ch$)$: # Return the index of the first $($leftmost$)$ occurrence of ch in str$,$ if any. Return $-1$ if ch does not occur in str$.$ for i in range$($len$($str$))$: if str$[$i$]==$ ch: return i return $-1$ def myRFind$($str$,$ ch$)$: # Return the index of the last $($rightmost$)$ occurrence of ch in str$,$ if any. Return $-1$ if ch does not occur in str$.$ for i in range$($len$($str$)-1,-1,-1)$: if str$[$i$]==$ ch: return i return $-1$ def myRemove$($str$,$ ch$)$: # Return a new string with the first occurrence of ch removed. If there is none, return str$.$ index $=$ str$.$find$($ch$)$ if index $!=-1$: return str$[$:index$]+$ str$[$index$+1$:$]$ return str def myRemoveAll$($str$,$ ch$)$: # Return a new string with all occurrences of ch removed. If there are none, return str$.$ return str$.$replace$($ch$,\text{'}\text{'})$ def myReverse$($str$)$: # Return a new string like str but with the characters in the reverse order. return str$[$::$-1]$ # Test cases s$1=$ "abcd" s$2=$ "efgh" print$($myAppend$($s$1,"$e$"))$ # 'abcde' print$($myCount$($s$1,"$e$"))$ # $0$ print$($myCount$($s$1,"$a$"))$ # $1$ print$($myCount$("$abcabc$","$a$"))$ # $2$ print$($myExtend$($s$1,$ s$2))$ # 'abcdefgh' print$($myMin$(""))$ # Empty string: no min value print$($myMin$("$zqralm$"))$ # $\text{'}$a$\text{'}$ print$($myMin$("$Hello World!"$))$ # $\text{'}\text{'}$ print$($myInsert$("$abc$",0,"$d$"))$ # 'dabc' print$($myInsert$("$abc$",2,"$d$"))$ # 'abdc' print$($myInsert$("$abc$",4,"$d$"))$ # Invalid index print$($myPop$("$abcd$",1))$ # $(\text{'}$acd$\text{'},\text{'}$b$\text{'})$ print$($myPop$("$abcd$",0))$ # $(\text{'}$bcd$\text{'},\text{'}$a$\text{'})$ print$($myPop$("$abcd$",5))$ # Invalid index print$($myFind$("$abcdabcd$","$a$"))$ # $0$ print$($myFind$("$abcdabcd$","$c$"))$ # $2$ print$($myFind$("$abcdabcd$","$f$"))$ # $-1$ print$($myRFind$("$abcdabcd$","$d$"))$ # $7$ print$($myRFind$("$abcdabcd$","$e$"))$ # $-1$ print$($myRemove$("$abcdabcd$","$a$"))$ # 'bcdabcd' print$($myRemove$("$abcdabcd$","$x$"))$ # 'abcdabcd' print$($myRemove$("$abcdabcd$","$d$"))$ # 'abcabcd' print$($myRemoveAll$("$abcabcabca$","$a$"))$ # $\text{'}$bcbcbc$\text{'}$ print$($myReverse$("$abcd$"))$ # 'dcba' print$($myReverse$(""))$ # $\text{'}\text{'}$