Guido van Rossum (the original creator of the Python language) decided to clean up Python 2.x properly, with less regard for backwards compatibility than is the case for new releases in the 2.x range. The most drastic improvement is the better Unicode support (with all text strings being Unicode by default) as well as saner bytes/Unicode separation.
Besides, several aspects of the core language (such as print and exec being statements, integers using floor pision) have been adjusted to be easier for newcomers to learn and to be more consistent with the rest of the language, and old cruft has been removed (for example, all classes are now new-style, "range()" returns a memory efficient iterable, not a list as in 2.x).
py2与3的详细区别
PRINT IS A FUNCTION
The statement has been replaced with a print() function, with keyword arguments to replace most of the special syntax of the old statement (PEP 3105). Examples:
Old: print "The answer is", 2*2 New: print("The answer is", 2*2)
Old: print x, # Trailing comma suppresses newline New: print(x, end=" ") # Appends a space instead of a newline
Old: print # Prints a newline
New: print() # You must call the function!
Old: print >>sys.stderr, "fatal error" New: print("fatal error", file=sys.stderr)
Old: print (x, y) # prints repr((x, y))
New: print((x, y)) # Not the same as print(x, y)! ALL IS UNICODE NOW
从此不再为讨厌的字符编码而烦恼
还可以这样： (A,*REST,B)=RANGE(5)
<strong>>>> a,*rest,b = range(5) >>> a,rest,b (0, [1, 2, 3], 4) </strong>
One popular module that don't yet support Python 3 is Twisted (for networking and other applications). Most
actively maintained libraries have people working on 3.x support. For some libraries, it's more of a priority than
others: Twisted, for example, is mostly focused on production servers, where supporting older versions of
Python is important, let alone supporting a new version that includes major changes to the language. (Twisted is
a prime example of a major package where porting to 3.x is far from trivial
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