Python - ValueError：无法将字符串转换为浮点数：[9000]

Question

我想了解此错误消息（Python 2.7）。我发现以前有人问过这个问题，但我不明白给出的解释，所以我再次问。

这里是我的代码：

import re 
name = raw_input("Enter file:") 
if len(name) < 1 : name = "file.txt" 
handle = open(name) 
y = list() 
for line in handle: 
    line = line.rstrip() 
    if re.findall('[0-9]+', line) != [] :   
     y.append(re.findall('[0-9]+', line)) 
a = [map(int, b) for b in y] 
for x in range(len(a)): 
    if len(a[x]) == 1: 
     b=str(a[x]) 
     c=float(b) 

Answer 1

你会看到发生了什么，如果你打印次数多

您已经创建名单

列表，这样一个[X]本身就是一个列表

当您将其列表化为列表时，它的'[9000]'

so yo你不能浮出水面，因为它不是一个数字

你将不得不去掉括号;或无法创建一个列表的列表使用您的文章作为输入与

开始：

import re 
handle = ''' 
Python - ValueError: could not convert string to float: [9000] 
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I am trying to understand this error message (Python 2.7). I see there are 
others who have asked this question previously, but I do not understand the 
explanations given there so I am asking again. Here is my code. Yes, I am a 
newbie trying to learn the basics so please keep that in mind when you answer. 
There's a reason I haven't been able to understand previous posts. 
''' 
y = list() 
print y 
for line in handle: 
    line = line.rstrip() 
    if re.findall('[0-9]+', line) != [] :   
     y.append(re.findall('[0-9]+', line)) 

print y 
a = [map(int, b) for b in y] 
print a 
for x in range(len(a)): 
    if len(a[x]) == 1: 
     b=str(a[x]) 
     print b 
     c=float(b) 

回报：

[] 
[['9'], ['0'], ['0'], ['0'], ['0'], ['2'], ['7']] 
[[9], [0], [0], [0], [0], [2], [7]] 
[9] 
Traceback (most recent call last): 
    File "test4.py", line 31, in <module> 
    c=float(b) 
ValueError: could not convert string to float: [9] 

我不知道你的最终目标是什么，但如果你这样做：

b=str(a[x][0]) 
print b 
c=float(b) 

它会工作，并返回

9 
0 
0 
0 
0 
2 
7