Seite - 87 - in Programming for Computations – Python - A Gentle Introduction to Numerical Simulations with Python 3.6, Band Second Edition

4.1 Functions:HowtoWriteThem? 87 function argumentf insum_funcion_values(f, start, stop)will act as the local“nick-name”(insidethefunctionsum_funcion_values)foranyfunctionthat isusedasfirst argumentwhencallingsum_funcion_values. Executing theprogram,gives theexpectedprintoutas Sum with f becomes 6 Sum with g becomes 14 4.1.9 LambdaFunctions A one-line function may be defined in a compact way, as a so-called lambda function.Thismaybe illustratedas g = lambda x: x**2 # ...which is equivalent to: def g(x): return x**2 Lambda functions are particularly convenient as function arguments, as seen next, whencallingsum_function_valuesfromabovewith lambdafunctionsreplacing the functionsfandg: print(sum_function_values(lambda x: x, 1, 3)) print(sum_function_values(lambda x: x**2, 1, 3)) This gives the same output as we got above. In this way, the lambda function is defined “in” the function call, so we avoid having to define the function separately prior to the (function)call. A lambda function may take several comma-separated arguments. A more general formofa lambdafunction is thus function_name = lambda arg1, arg2, ... : <some_expression> # ...which is equivalent to: def function_name(arg1, arg2, ...): return <some_expression> The general syntax consists of the reserved wordlambda, followed by a series of parameters, thenacolon,and,finally,somePythonexpressionresultinginanobject tobe returnedfromthe function. 4.1.10 AFunctionwithSeveralReturnStatements It ispossible tohaveseveralreturnstatements ina function,as illustratedhere: def check_sign(x): if x > 0: return ’x is positive’ elif x < 0: return ’x is negative’ else: return ’x is zero’