您应该避免使用python错误（以及如何修复它们！）

<code class="python">def add_item(item, my_list=[]):
    my_list.append(item)
    return my_list

print(add_item(1))  # [1]
print(add_item(2))  # [1, 2] (意料之外的结果!)</code>

<code class="python">def add_item(item, my_list=None):
    if my_list is None:
        my_list = []
    my_list.append(item)
    return my_list</code>

<code class="python">nums = [1, 2, 3, 4]
for n in nums:
    if n % 2 == 0:
        nums.remove(n)</code>

<code class="python">nums = [n for n in nums if n % 2 != 0]</code>

<code class="python">if my_var == None:
    print("找到了None")</code>

<code class="python">if my_var is None:
    print("找到了None")</code>

<code class="python">if x = 5:  # SyntaxError!
    print("x 等于 5")</code>

<code class="python">if x == 5:
    print("x 等于 5")</code>

<code class="python">for i in range(len(my_list)):
    print(i, my_list[i])</code>

<code class="python">for index, value in enumerate(my_list):
    print(index, value)</code>

<code class="python">words = ["python", "is", "awesome"]
sentence = ""
for word in words:
    sentence += word + " "</code>

<code class="python">sentence = " ".join(words)</code>