Seite - 14 - in Programming for Computations – Python - A Gentle Introduction to Numerical Simulations with Python 3.6, Band Second Edition

14 1 TheFirstFewSteps Alternatively, we could use the import statement import math. This would require atan and pi to be prefixed with math, however, as shown in ball_angle_prefix.py: import math x = 10.0 # Horizontal position y = 10.0 # Vertical position angle = math.atan(y/x) print (angle/math.pi)*180 The essential difference between the two import techniques shown here, is the prefix requiredby the latter. Both techniquesare commonlyused and represent the two basic ways of importing library code in Python. Importing code is an evident partofPythonprogramming,sowe better shedsomemore lighton it. 1.4 ImportingfromModulesandPackages At first, it may seem cumbersometo havecode in different libraries, since it means you have to know (or find out) what resides in which library.10 Also, there are many libraries around in addition to the Python standard library itself. To your comfort, you come a long way with just a few libraries, and for easy reference, the handfulof librariesusedinthisbookis listedbelow(Sect.1.4.5).Havingeverything available at any time would be convenient,but this would also mean that computer memorywouldbefilledwithalotofunusedinformation,causinglessmemorytobe available forcomputationsonbigdata.Pythonhasso manylibraries,with so much functionality, that importingwhat isneeded is indeeda verysensible strategy. Where to Place Import Statements? The general recommendation is to place import statementsat the topofaprogram,making themeasy tospot. 1.4.1 ImportingforUseWithoutPrefix Theneed toprefix itemnames is avoidedwhen import statementsareon the form from some_library import ... # i.e., items will be used without prefix as we saw in ball_angle.py above. Without prefixing, coded formulas often becomeeasier toread,sincecodegenerallycomes“closer”tomathematicalwriting. Ontheotherhand,it is lessevidentwhereimporteditems“comefrom”andthismay complicate matters, particularly when trying to understand more comprehensive codewrittenbyothers. 10 There is a built-in function calleddir, which gives all the names defined in a library module. Another built-in function called help prints documentation. To see how they work, write (in Spyder, pane down to the right)import math followed bydir(math)orhelp(math).