无法获取用作列表理解的for循环

Question

这个for循环可以正常工作，但不能作为列表理解。 理解为每个迭代创建空元素。 有人能解释什么是错误的以及如何修复它吗

def GetAsciiList():
    num_list = []
    for num in range(32, 42, 1):
        num_list.append((str(num), chr(num)+" "))
    return num_list

def GetAsciiListLC():
    num_list = []
    num_list = [(num_list.append((str(num), chr(num)+" "))) for num in range(32, 42, 1)]
    return num_list

print GetAsciiList()
print GetAsciiListLC()

---

控制台输出：

[('32', '  '), ('33', '! '), ('34', '" '), ('35', '# '), ('36', '$ '), ('37', '% '), ('38', '& '), ('39', "' "), ('40', '( '), ('41', ') ')]
[None, None, None, None, None, None, None, None, None, None]

Answer 1

在{{CD1}}中考虑此行：

num_list = [(num_list.append((str(num), chr(num)+" "))) for num in range(32, 42, 1)]

num_list.append((str(num), chr(num)+" ")))对列表进行变异并返回None

我想你想要的是：

def GetAsciiListLC():
    """ Return list of 2-tuples containing numbers and ASCII equivalents, both as strings. """
    return [(str(num), chr(num) + " ") for num in range(32, 42)]

有关从list.append（）方法返回None的基本原理，请参见此问题： Why does append() always return None in Python?