Seite - 29 - in Programming for Computations – Python - A Gentle Introduction to Numerical Simulations with Python 3.6, Band Second Edition

1.6 Plotting,PrintingandInputData 29 So, make sure the order of the arguments is correct. An alternative is to name the arguments. Naming the Arguments If we name the arguments (v1 andv2 are arguments to format),we get thecorrectprintoutwhetherwe callprintas print(’v1 is {v1}, \nv2 is {v2}’.format(v1=v1, v2=v2)) or, switching theorder, print(’v1 is {v1}, \nv2 is {v2}’.format(v2=v2, v1=v1)) Note that the names introduced do not have to be the same as the variable names, i.e., “any” names would do. Thus, if we (for the sake of demonstration) rather use the namesa andb, anyof the followingcalls toprintwould work just asfine (try it!): print(’v1 is {a}, \nv2 is {b}’.format(a=v1, b=v2)) or print(’v1 is {a}, \nv2 is {b}’.format(b=v2, a=v1)) Controlling the printout like we have demonstrated this far, may be sufficient in many cases. However, as we will see next, even more printing details can be controlled. Formatting More Details Often, we want to control how numbers are formatted. For example, we may want to write 1/3 as0.33 or 3.3333e-01 (3.3333 ·10−1), andas thefollowingexamplewilldemonstrate,suchdetailsmayindeedbespecified in the argument to print. The essential new thing then, is that we supply the placeholders{}withsomeextra informationin between thebrackets. Suppose we have a real number 12.89643, an integer 42, and a text ’some message’ thatwe want to writeout in the following twodifferentways: real=12.896, integer=42, string=some message real=1.290e+01, integer= 42, string=some message The real number is first to be written in decimal notation with three decimals, as 12.896,butafterwardsinscientificnotationas1.290e+01.Theintegershouldfirst be written as compactly as possible, while the second time,42 should be placed in afivecharacterwide textfield. The followingprogram,formatted_print.py,produces the requestedoutput: r = 12.89643 # real number i = 42 # integer s = ’some message’ # string (equivalent: s = "some message") print(’real={:.3f}, integer={:d}, string={:s}’.format(r, i, s)) print(’real={:9.3e}, integer={:5d}, string={:s}’.format(r, i, s)) Here,eachplaceholdercarriesaspecificationofwhatobject type thatwillenterin thecorrespondingplace,withf symbolizingafloat (realnumber),d symbolizing anint (integer), ands symbolizingastr (string). Also, there is a specification of how each number is to be printed. Note the colon within the brackets, it must be there!