蟒蛇。ValueError无法将字符串转换为浮点型:

2022-04-05 00:00:00 python spyder

问题描述

我正在尝试生成文本文件中指定列中数字的平均值。我收到了一个错误,即虽然我不知道我可以在哪里向它传递无效的字符串,但Python无法将字符串转换为浮点型。

def avg_col(f, col, delim=None, nhr=0):
    """
    file, int, str, int -> float

    Produces average of data stored in column col of file f

    Requires: file has nhr header rows of data; data is separated by delim

    >>> test_file = StringIO('0.0, 3.5, 2.0, 5.8, 2.1')
    >>> avg_col(test_file, 2, ',', 0)
    2.0

    >>> test_file = StringIO('0.0, 3.5, 2.0, 5.8, 2.1')
    >>> avg_col(test_file, 3, ',', 0)
    5.8
    """
    total = 0 
    count = 0


    skip_rows(f, nhr)
    for line in f: 
        if line.strip() != '':
            data = line.split(delim)
            col_data = data[col]
            total = sum_data(col_data) + total
            count = len(col_data) + count 
    return total / count

def sum_data(lod):
    '''
    (listof str) -> Real 

    Consume a list of string-data in a file and produce the sum

    >>> sum_data(['0'])
    0.0
    >>> sum_data(['1.5'])
    1.5

    '''
    data_sum = 0
    for number in lod: 
        data_sum = data_sum + float(number)
    return data_sum

解决方案

您正在将一个字符串传递给sum_lod()

data = line.split(delim)
col_data = data[col]
total = sum_data(col_data) + total

data是字符串列表,data[col]是一个元素。

sum_data()另一方面,需要可迭代:

def sum_data(lod):
    # ...
    for number in lod: 

迭代一个数字,然后得到各个字符:

>>> for element in '5.8':
...     print element
... 
5
.
8

尝试转换此类字符串的每个元素很容易导致您尝试将非数字的字符转换为浮点型:

>>> float('.')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: could not convert string to float: .

传入字符串列表:

total += sum_data([col_data])
count += 1

或只在您拥有的一个元素上使用float()

total += float(col_data)
count += 1

相关文章