functionsscopingand abstraction the point of execution (the next instruction to be executedmoves from the point of invocation to the first statement in the body of the function the code in the body of the function is executed until either return statement is encounteredin which case the value of the expression following the return becomes the value of the function invocationor there are no more statements to executein which case the function returns the value none (if no expression follows the returnthe value of the invocation is none the value of the invocation is the returned value the point of execution is transferred back to the code immediately following the invocation parameters provide something called lambda abstraction, allowing programmers to write code that manipulates not specific objectsbut instead whatever objects the caller of the function chooses to use as actual parameters finger exercisewrite function isin that accepts two strings as arguments and returns true if either string occurs anywhere in the otherand false otherwise hintyou might want to use the built-in str operation in keyword arguments and default values in pythonthere are two ways that formal parameters get bound to actual parameters the most common methodwhich is the only one we have used thus faris called positional--the first formal parameter is bound to the first actual parameterthe second formal to the second actualetc python also supports what it calls keyword argumentsin which formals are bound to actuals using the name of the formal parameter consider the function definition in figure the function printname assumes that firstname and lastname are strings and that reverse is boolean if reverse =trueit prints lastnamefirstnameotherwise it prints firstname lastname def printname(firstnamelastnamereverse)if reverseprint lastname 'firstname elseprint firstnamelastname figure function that prints name each of the following is an equivalent invocation of printnameprintname('olga''puchmajerova'falseprintname('olga''puchmajerova'falseprintname('olga''puchmajerova'reverse falseprintname('olga'lastname 'puchmajerova'reverse falseprintname(lastname='puchmajerova'firstname='olga'reverse=false the name "lambda abstractionis derived from some mathematics developed by alonzo church in the and