<pre><code>numOfYears = 0
cpi = eval(input("Enter the CPI for July 2015: "))
if cpi.isdigit():
while cpi < (cpi * 2):
cpi *= 1.025
numOfYears += 1
print("Consumer prices will double in " + str(numOfYears) + " years.")
while not cpi.isdigit():
print("Bad input")
cpi = input("Enter the CPI for July 2015: ")
</code></pre>
<p>我得到以下错误。</p>
<blockquote>
<p>AttributeError: 'int' object has no attribute 'isdigit'</p>
</blockquote>
<p>因为我是编程新手,我真的不知道它想告诉我什么。我正在使用<code>if cpi.isdigit():</code>检查用户输入的是不是一个有效数字。</p>