#!/usr/bin/env python
# coding: utf-8

# ## 复现 bug

# ### print_iterator

# 定义 `print_iterator`

# In[1]:


def print_iterator(iterator):
    while True:
        try:
            element = next(iterator)
        except StopIteration:
            break
        else:
            print(element)


# 测试 print_iterator

# In[3]:


print_iterator(iter([1, 2, 3]))


# 工作完全正常

# ### counter_iterable

# 定义 counter_iterable

# In[7]:


def counter_iterable(iterable):
    iterator = iter(iterable)
    iterator_length = sum(1 for _ in iterator)

    print(iterator_length)


# 测试 counter_iterable

# In[6]:


counter_iterable([1, 2, 3])


# 工作完全正常

# ### 组合在一起

# 定义 counter_iterable_and_print

# In[9]:


def counter_iterable_and_print(iterable):
    iterator = iter(iterable)
    iterator_length = sum(1 for _ in iterator)

    print(iterator_length)

    print_iterator(iterator)


# 测试 counter_iterable_and_print

# In[10]:


counter_iterable_and_print([1, 2, 3])


# <span style="color:red">工作不正常！</span>

# ## 原因

# `iterator` 内有有状态信息，具有不可重入（non-reentrant）的特性，这个和 `list`, `tuple`, `dict` 等容器不一样，容器通过 `__getitem__` 来迭代。

# 示例代码：

# In[12]:


iterable = [1, 2, 3]
iterator = iter(iterable)
iterator_length = sum(1 for _ in iterator)
iterator_length_2 = sum(1 for _ in iterator)


# In[13]:


print(iterator_length)
print(iterator_length_2)


# ## 解决方案

# 每次循环都重新生成一个 iterator 对象

# In[14]:


iterable = [1, 2, 3]

iterator = iter(iterable)
iterator_length = sum(1 for _ in iterable)

iterator = iter(iterable)
iterator_length_2 = sum(1 for _ in iterable)


# In[15]:


print(iterator_length)
print(iterator_length_2)