try: from simplejson import dumps as json_dumps, loads as json_lds except ImportError: # pragma: no cover try: from json import dumps as json_dumps, loads as json_lds except ImportError: try: from django.utils.simplejson import dumps as json_dumps, loads as json_lds except ImportError: def json_dumps(data): raise ImportError("JSON support requires Python 2.6 or simplejson.") json_lds = json_dumps # We now try to fix 2.5/2.6/3.1/3.2 incompatibilities. # It ain‘t pretty but it works... Sorry for the mess. py = sys.version_info py3k = py >= (3, 0, 0) py25 = py < (2, 6, 0) py31 = (3, 1, 0) <= py < (3, 2, 0) # Workaround for the missing "as" keyword in py3k. def _e(): return sys.exc_info()[1] # Workaround for the "print is a keyword/function" Python 2/3 dilemma # and a fallback for mod_wsgi (resticts stdout/err attribute access) try: _stdout, _stderr = sys.stdout.write, sys.stderr.write except IOError: _stdout = lambda x: sys.stdout.write(x) _stderr = lambda x: sys.stderr.write(x)
这段代码，主要是有三块：
第一部分，定义json的dumps和loads，尝试各个模块，如果都没有，就报错
第二部分，确定python的版本
第三部分通过lambda定义
_stdout和_stderr
_stdout = lambda x: sys.stdout.write(x)
可以理解为：
def _stdout(x):
sys.stdout.write(x)
原文：http://www.cnblogs.com/aomi/p/7019665.html