$.$ Write a function named productDigit$($s$)$ that accepts a string s as the argument. Assume this string contains a series of single$-$digit numbers. Use a for loop to loop through each character in the string, then calculate and return the product of all the single$-$digit numbers in the string. For example, if the argument is $\text{'}1357\text{'},$ your function should return $105,$ because $1$x$3$x$5$x$7=105.(25$ pts$)$

Write a function named productDigit$($s$)$ that accepts a string s as the argument. Assume this string contains a series of single$-$digit numbers. Use a for loop to loop through each character in the string, then calculate and return the product of all the single$-$digit numbers in the string. For example, if the argument is $\text{'}1357\text{'},$ your function should return $105,$ because $1$x$3$x$5$x$7=105.(25$ pts$)$