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Python from novice to pro
You're already familiar with using list comprehensions to map one list into another. There is another way to accomplish the same thing, using the built-in map function. It works much the same way as the filter function.
Example 16.10. Introducing map
>>> def double(n): ... return n*2 ... >>> li = [1, 2, 3, 5, 9, 10, 256, -3] >>> map(double, li) [2, 4, 6, 10, 18, 20, 512, -6] >>> [double(n) for n in li] [2, 4, 6, 10, 18, 20, 512, -6] >>> newlist =  >>> for n in li: ... newlist.append(double(n)) ... >>> newlist [2, 4, 6, 10, 18, 20, 512, -6]
|map takes a function and a list and returns a new list by calling the function with each element of the list in order. In this case, the function simply multiplies each element by 2.|
|You could accomplish the same thing with a list comprehension. List comprehensions were first introduced in Python 2.0; map has been around forever.|
|You could, if you insist on thinking like a Visual Basic programmer, use a for loop to accomplish the same thing.|
Example 16.11. map with lists of mixed datatypes
All right, enough play time. Let's look at some real code.
Example 16.12. map in regression.py
filenameToModuleName = lambda f: os.path.splitext(f) moduleNames = map(filenameToModuleName, files)
|As you saw in Section 4.7, “Using lambda Functions”, lambda defines an inline function. And as you saw in Example 6.17, “Splitting Pathnames”, os.path.splitext takes a filename and returns a tuple (name, extension). So filenameToModuleName is a function which will take a filename and strip off the file extension, and return just the name.|
|Calling map takes each filename listed in files, passes it to the function filenameToModuleName, and returns a list of the return values of each of those function calls. In other words, you strip the file extension off of each filename, and store the list of all those stripped filenames in moduleNames.|
As you'll see in the rest of the chapter, you can extend this type of data-centric thinking all the way to the final goal, which is to define and execute a single test suite that contains the tests from all of those individual test suites.
 Again, I should point out that map can take a list, a tuple, or any object that acts like a sequence. See previous footnote about filter.
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