擅长:python、mysql、java
<p>您正在使用<code>unit</code>而不是<code>value</code>。还要注意你的<code>if</code>和<code>input</code>的区别。还建议使用<code>elif</code>:</p>
<pre><code>unit = input(str("is your speed in mph or kmh? ")).lower()
value = float(input("what is your speed? "))
if unit == 'mph':
result = str(value * 1.6) + 'kmh'
elif unit == 'kmh':
result = str(value / 1.6) + 'mph'
print(result)
else:
pass
print(value, unit, "is equal to ", result)
</code></pre>