为什么我不能将 str 列表转换为浮点列表？答案

【问题标题】：Why I can't convert a list of str to a list of floats?为什么我不能将 str 列表转换为浮点列表？
【发布时间】：2011-08-22 22:08:21
【问题描述】：

我开始写代码，但是一开始就失败了。

这是我的代码：

import csv
reader = csv.reader(open("QstartRefseqhg19.head"), dialect='excel-tab' )

for row in reader:
    C = row[1].split(",")[1:]
    C1 = [float(i) for i in C]

    print C1

错误日志显示：

Traceback (most recent call last):
  File "/home/geparada/workspace/SJtag/src/TagGen.py", line 8, in <module>
    C1 = [float(i) for i in C]
ValueError: empty string for float()

我也试过了

import csv
reader = csv.reader(open("QstartRefseqhg19.head"), dialect='excel-tab' )

for row in reader:
    C = row[1].split(",")[1:]       
    C1 = map(float, C)        

    print C1

我的输入文件如下所示：

NM_032291   0,227,291,316,388,445,500,676,688,700,725,777,863,956,1031,1532,1660,1787,1847,1959,2115,2248,2451,2516,2681,   tttctctcagcatcttcttggtagcctgcctgtaggtgaagaagcaccagcagcatccatggcctgtcttttggcttaacacttatctcctttggctttgacagcggacggaatagacctcagcagcggcgtggtgaggacttagctgggacctggaatcgtatcctcctgtgttttttcagactccttggaaattaaggaatgcaattctgccaccatgatggaaggattgaaaaaacgtacaaggaaggcctttggaatacggaagaaagaaaaggacactgattctacaggttcaccagatagagatggaattcagcccagcccacacgaaccaccctacaatagcaaagcagagtgtgcgcgtgaaggaggaaaaaaagtttcgaagaaaagcaatggggcaccaaatggattttatgcggaaattgattgggaaagatataactcacctgagctggatgaagaaggctacagcatcagacccgaggaacccggctctaccaaaggaaagcacttttattcttcaagtgaatcggaagaagaagaagaatcacataagaaatttaatatcaagattaaaccattgcaatctaaagacattcttaagaatgctgcaactgtagatgaattgaaggcatcaataggcaacatcgcactttccccatcaccagtgaggaaaagtccgaggcgcagcccgggtgcaattaaaaggaacttatccagtgaagaagtggcaagacccaggcgttccacaccaactccagaacttataagcaaaaagcctccagatgacactacggcccttgctcctctctttggcccaccactagaatcagcttttgatgaacagaagacagaagttcttttagatcagcctgagatatggggttcaggccaaccaattaatccaagcatggagtcgccaaagttaacaaggccttttcccactggaacacctccaccactgcctccaaaaaatgtaccagctaccccaccccgaacaggatcccccttaacaattggaccaggaaatgaccagtcagccacagaggtcaaaattgaaaaactaccatccatcaatgacttggacagcatttttgggccagtattgtcccccaagtctgttgctgttaatgctgaagaaaagtgggtccatttttctgatacatccccggaacatgttactccggagttgactccaagggaaaaagtggtgtccccaccagctacaccagacaacccagctgactccccagctccaggccctctcggccccccaggtcccacaggccccccagggcctcctgggcctcctcgcaatgtactatcgccgctcaatttagaagaagtccagaagaaagtcgctgagcagaccttcattaaagatgattacttagaaacaatctcatctcctaaagattttgggttgggacaaagagcaactccacctcccccaccaccacccacctacaggactgtggtttcgtcccccggacctggctcgggccctggtccggggaccaccagtggtgcatcatcccctgctcgaccagccactcctttggttccttgcagaagtaccactccacctccacctcctccccggcctccatcccggccaaagctacctccaggaaaacctggagttggagatgtgtccagaccttttagccctcccattcattcttccagccctcctccaatagcacccttagcgcgggctgaaagcacttcttcaatatcgtcaaccaattccttgagcgcagccaccactcccacagttgagaatgaacagccttccctcgtttggtttgacagaggaaagttttatttgacttttgaaggttcttccaggggacccagccccctaaccatgggagctcaggacactctccctgttgcagcagcatttacagaaacagtcaatgcctatttcaaaggagcagacccaagcaaatgtatcgttaagattaccggagaaatggtgttgtcatttcctgctggcatcaccagacactttgccaacaacccgtccccagctgctctgacttttcgggtgataaatttcagcaggttagaacacgtcctgccaaacccccaacttctctgctgtgataatacacaaaatgatgccaataccaaggaattctgggtaaacatgccaaatttgatgactcacctaaagaaagtgtctgaacaaaaaccccaggctacatattataacgttgacatgctcaaatatcaggtgtctgcccagggcattcagtccacacctctgaacctggcagtgaattggcgatgtgagccttcaagcactgacctgcgcatagattacaaatataatacagatgcaatgacgactgctgtggccctcaacaatgtgcagttcctggtccccatcgacggaggagtcaccaagctccaggcagtgctcccaccagcagtctggaatgctgaacaacagagaatattgtggaagattcctgatatctctcagaagtcagaaaatggaggggtgggttctttgttggcaagatttcagttatctgaaggcccaagcaaaccttctccattggttgtgcagttcacaagtgaaggaagcaccctttctggctgtgacattgaacttgttggagcagggtatcgattttcactcatcaagaaaaggtttgctgcaggaaaatacttggcagataactaatgaaatcttatgcaaggatttggaggattcatataatggagaactgatgtatgagaaacagattttaattttggtttgatgaaaacaaaccaatatctgcacttgggatatatcaggtggaaagtcaatgactttcatctgtgatttccctcacacactaccatgatgaccagtcctacagtatttacttctaggtgtaatattgttaatggttttaaaatgtaattattgtatttgtaaattgtactctcattccagtaaggcagttagacacttgagttttagcattttaccattcctgaaatggatgtaatttaaactgtggtatgtaaatttaatagtagtattgttgaatggcacaatgcttacagaggtagattgcattttgtcaatatataaaatttaaatataatattgatagctgtcataaagggggtgccacatattaaagaaacttaagtggaaccagaagaaaaagaaacaaacttacttttcttcaatgcttagtatgttttactctagtgctaaataaaaactctatcttcaaatgtttagtgggttaaattgagaaactatttcagaaaaaaattctaaggttacagcatattcaaagaaaagcattagttaccactttttaaaaagcttttttttcaaactgcaaatttcataaaaatgcaaactgtgtaaacagggcctcttatttttataacttgtgtaaaaagggaaagcaattcatatttaaagtttaagtatattaaattataatcaagagtaaagaagatgttgaagtcttaactacttgcccctctctacagtttcgcaaatgtggggattgctgaataatcagtcagactaaaaccaaaattgtgattttaagatttcaagactttccgtagttgaactggttaagaatttttgcttagttactctgaatagatgatcttactcatccagtatgggggaatgatacctcacgtcttcctctttacccacaggaatcaaaacgctgagactgagaattttagggaaaaaaaagtccactgtttagatccagaaggagagttttaatcattgtttatatcatttgagaatgaaaaaataagcttcataaatgaaattctattcacattactgtgtaataaatttccttttggatgattaggattcattgtataaaactgtaaatctttgccattcttggagaagcaaaaggagagttatcaaaaatgtatgtcgtttcatcgttgcaaggtataataaaaactgtaattattcaatctggccctgccatatgaacatttagaaagacaaacttcttcgggagtctcagttgtaaaaccttccctcattaatatctgaaaatgttagtcttcctttaagtcatagaacttatttaaacataaaccaatttctattacaggttatgctattaaatagctgtaattattaagttattatttttataattagttgttaaatttcattttacacccactcaaatttaacaaagaatctttagcccctttaaattttagaattaaattaaatttttaaagttttacttctaaaatgagattgtgactggcaattgtttatagtgaaactttttaaattaatctttgtactcctctatcagtgcttgctaccaagagaatgtccaaaatgatttgttttaccatgggaaaattcttactattcaacaaactctcagttggccccctacagcagtctggtgttgaagtttctttgaacgaactaaatatactcattttatgtaaaggtatccaatttgattttgaaaccaaaatagaaaatgcaaaattctaaattccatgaaacatggaatttatgacaccaaaatcaatggagagtaagcagcagcaaactgagaattatccagcatatgaatataacaatgtgtttttaagtaatcaattcatttaaaaaattgaatattaatacaaagcatattaaaaacatgtaaatatta
NM_001080397    0,397,490,715,1443,1597,1774,1980,  atgatccccgcagccagcagcaccccgccgggagatgccctcttccccagcgtggccccacaggacttctggaggtcccaggtcacgggctactcggggtccgtgacacgacacctcagtcaccgggccaacaacttcaaacgacaccccaagaggaggaagtgcattcgtccctccccacccccgccccccaacaccccgtgcccgcttgagctggtggacttcggggacctgcacccccagaggtccttccgggagctgcttttcaacggctgcattctctttggcatcgagttcagctacgccatggagacggcgtacgtgaccccggtgctcctgcagatgggcctgcccgaccagctctacagcctggtgtggttcatcagccccatcctcggattcctactgcagcctctgttgggtgcttggagtgaccggtgtacctcaaggtttggaaggagacgccctttcattcttgtcctggctataggggcactgctgggcctctcgctcttgctgaatggccgggacattggcatcgccctggctgacgtgaccgggaaccacaagtggggcctgctgctgaccgtgtgcggtgtggtgctgatggactttagcgccgactcggcggacaaccccagccacgcctacatgatggacgtgtgcagccccgcagaccaggaccgaggcctgaacatccacgccctcctggcaggtctcggaggaggctttggatacgtggtcggcggaatccactgggataaaacgggcttcgggagggccctggggggacagctccgagtcatttacctcttcactgcggtcaccctgagcgtcaccaccgtcctgaccctggtcagcatccctgagaggccgctgcggccgccgagtgagaagcgggcagccatgaagagccccagcctcccgctgcccccgtccccacccgtcctgccagaggaaggccctggcgacagcctcccgtcgcacacggccaccaacttctccagccccatctcgccgcccagccccctcacgcccaagtacggcagcttcatcagcagggacagctccctgacgggcatcagcgagttcgcctcatcctttggcacggccaacatagacagcgtcctcattgactgcttcacgggcggccacgacagctacctggccatccctggcagcgtccccaggccgcccatcagcgtcagcttcccccgggcccccgacggcttctaccgccaggaccgtggacttctggagggcagagagggtgccctgacctccggctgtgacggggacattctgagggtgggctccttggacacctctaagccgaggtcatcagggattctgaagagacctcagaccttggccatcccggacgcagccggaggagggggtcccgaaaccagcaggagaaggaatgtgaccttcagtcagcaggtggccaatatcctgctcaacggcgtgaagtatgagagcgagctgacgggctccagcgagcgcgcggagcagcctctgtccgtggggcgcctctgctccaccatctgcaacatgcccaaggcgctacgcaccctctgcgtcaaccacttcctggggtggctctcattcgaggggatgttgctcttctacacagacttcatgggcgaggtggtgtttcagggggaccccaaggccccgcacacatcagaggcgtatcagaagtacaacagcggcgtgaccatgggctgctggggcatgtgtatctacgccttcagtgctgccttctactcagctatcctggagaagctggaggagttcctcagcgtccgcaccctctacttcatcgcctatctcgccttcggcctggggaccgggcttgccaccctctccaggaacctctacgtggtcctgtcgctctgcataacctacgggattttattttccaccctgtgcaccttgccttactcgctgctctgcgattactatcagagtaagaagtttgcagggtccagtgcggacggcacccggcggggcatgggcgtggacatctctctgctgagctgccagtacttcctggctcagattctggtctccctggtcctggggcccctgacctcggccgtgggcagtgccaacggggtgatgtacttctccagcctcgtgtccttcctgggctgcctgtactcctccctgtttgtcatttatgaaattcctcccagcgacgctgcagacgaggagcaccggcccctcctgctgaacgtctgacatcgcggagcctcgactccggacacgcgcctgcacctgggggtctggagcaggccgaccagtgaggaccaaagggccttgttggacagggggactggctgcctactggaatgtaaatatgtgataaaataataaatgacagcggcaaagccta
NM_001145277    0,182,283,388,470,579,757,  gaaacctggtcagagagtcgcaccgcttccgtccgtcggacagaggaacggtggaagtcgccggaagttcggtgggctccaggcgtcgcgatggaggagagcgggtacgagtcggtgctctgtgtcaagcctgacgtccacgtctaccgcatccctccgcgggctaccaaccgtggctacagggctgcggagtggcagctggaccagccatcatggagtggccggctgaggatcactgcaaagggacagatggcctacatcaagctggaggacaggacgtcaggggagctctttgctcaggccccggtggatcagtttcctggcacagctgtggagagtgtgacggattccagcaggtacttcgtgatccgcatcgaagatggaaatgggcgacgggcgtttattggaattggcttcggggaccgaggtgatgcctttgacttcaatgttgcattgcaggaccatttcaagtgggtgaaacagcagtgtgaatttgcaaaacaagcccagaacccagaccaaggccctaaactggacctgggcttcaaggagggccagaccatcaagctcaacatcgcaaacatgaagaagaaggaaggagcagctgggaatccccgagtccggcctgccagcacaggagggctgagcctgcttccccctcccccaggggggaaaacctccaccctgatccctccccctggggagcagttggctgtggggggatccctcgtccagccagcagttgctcccagttcagatcaacttccagccagacccagccaggcacaggctgggtccagttctgacctgagcacggtttttcctcatgtgacttctgggaaggcgctccctcatctgggccaaaggaaggaggacgaagccctcctcagctggcctgtgtttggggcatgaatctctcctctcctccttgtctggctctgttgacaaaccgggcatgtttggcagtaaattggcaccgtgtcacactgtttcctgggattcaagtatgcaaccagaacacaggagaagaaaagctccaggatccctgtccccatctgtcctcttgatgtgagagagactctgagacttcttccatcgcaatgacctgtattaaacacaagccccccaagcaaaagaagaggttgagtttgctgccaggattcagatcagcccttcccagggtctgcaggtgtcacatgatcacagttcagcgggaggctttccgtacccacactggctgtagccacttcagtccatctgccctccagaggaggggtttcttcctgatttttagcaggtttagaggctgcagcttgagctacaatcaggagggaaattggaaggattagcagcttttaaaaatgtttaaatattttgctttgctaatgtgctgatccgcactaactcatctttgcaaaaggaactgctccctcggcgtgccccagctggggcctctgaagggattcctcactgtgggcagctgccctgagcttcaggcagcagtgtttatctctggccagttgtctggtttccatgtattctaggccaggtaggcaacacagagccaaggcgggtgctggaagccagacggaacagtgttggggcaggaaggtggatgctgttgtcatggagctgtgggagttggcactctgtctgctggtggccctctcggctcacatgttcacagtgcagctcctggcagacttgggttttctctttggtggtttctaaagtgccttatctgcaaacaacttcttttctccttcaggaactgtgaatggctagaagaaggagctcagtaaactagaagtccagggttgcttggtttactggtttataagaaatctgaaagcacctctgacattccttttattaactcacctctcagttgaaagatttcttctttgaaaggtcaagaccgtgaactgaaaaaagtgttggcctttttgcgggaccagatttttaagataaaataaatatttttacttctgtcattgtatgtgaaaaaaaaaaaaa

我是堆栈，感谢您的时间！！

【问题讨论】：

调试提示：在失败语句之前，做print "C:", C

标签： python string list csv floating-point

【解决方案1】：

您的输入行以逗号结尾，例如：

0,182,283,388,470,579,757,

所以很自然，这将被拆分为：

['0', '182', '283', '388', '470', '579', '757', '']

最后一个元素总是一个空字符串''。你需要考虑到这一点。一种方法是简单地忽略它：

C1 = [float(i) for i in C if i]

或者通过在转换之前删除最后一个元素：

C = row[1].split(",")[1:-1]   # the slice will exclude first and last elements

【讨论】：

也可以先使用strip()方法：C = row[1].strip(',').split(',')[1:]
@Blair：我不得不这么说。感谢您指出了这一点。昨天我的心似乎在某个时候崩溃了。我希望它现在已修复。

【解决方案2】：

您可以在转换为浮点数并捕获 ValueErrors 时使用 try/except。

C = row[1].split(",")[1:] 
    for item in C:
    try:
        convert=float(item)
    except ValueError:
        print "not a number"

【讨论】：