To begin with let’s just have look at the old school of lambda in Python. As we know, lambda x: return x**2 is exactly equivalent to def squared(x): return x**2 Now look at this >>> f1 = lambda x,y,z: x+1, y+1, z+1 >>> print(f1(1,1,1)) What will you get on the screen? A tuple of (2, 2, 2)? No. You get an error instead. Traceback (most recent call last): File "<pyshell#7>", line 1, in <module> print(f1(1,1,1)) TypeError: 'tuple' object is not callable</module> Now that the “returning part” of lambda is covering the contents before comma only, let’s explicitly add the brackets:

As noted in Python 3 documention, behaviors of +, -, *, etc. can be redefined. Specially, I would like to take notes on some special yet common methods. __repr__ method This method is called when you apply print on the instance. Could be useful when debugging class related problems. __enter__, __exit__ methods Those two methods are key components of a context manager. Refer to https://jeffknupp.com/blog/2016/03/07/python-with-context-managers/ to get a sense on how to manage the fragile resouces with context manager.

简而言之，如果你通过Windows自带的命令提示符（cmd）启动了pip，并且看到了类似下面的错误提示 in console_to_strreturn s.decode(sys.__stdout__.encoding)UnicodeDecodeError: 'utf-8' codec can't decode byte 0xb6 in position 33: invalid start byte 多半是因