如何修复 ValueError ：无法将字符串转换为浮点数：在 Python 中

Question

我有一个从 CSV 文件读取并检查记录是否满足条件的 python 脚本。

• 如果是则系统显示结果
• 如果没有，系统会根据错误引发异常。

csv 文件包含一个具有浮点值的文件，但其中一些记录可能没有任何值，因此将为空。

问题是如果单元格为空，系统会显示此 ValueError ：

could not convert string to float: 

而不是我写的异常。

 raise Exception("this Record has empty value")

• row[0]==> 日期类型 Date
• row[10]==> 风速型浮子
• row[11]==> 雾类型布尔

代码：

import csv

mydelimeter = csv.excel()
mydelimeter.delimiter=";"
myfile = open("C:/Users/test/Documents/R_projects/homework/rdu-weather-history.csv")

# read the first line in the opened file ==> Header
myfile.readline()


myreader=csv.reader(myfile,mydelimeter)
mywind,mydate=[],[]
minTemp, maxTemp = [],[]
fastwindspeed, fog=[],[]

'''
create a variable that handle values of the 3 fields ==> Date - fastest5secwindspeed - fog
 and display the result where  
     fog ==> Yes    and highest speed  more than 10.
'''
for row in myreader:
    try:
        if row[11] =="Yes":
            if float(row[10]) < 10.0:
                raise Exception( 'the wind speed  is below 10 mph in ' + row[0] )
            if row[10] in (None, ""):
                raise Exception("this Record has empty value")

            print(row[0],row[10],row[11])
    except Exception as e:
        print("{}".format(e))

myfile.close()

Answer 1

您可以更改加注的顺序，同时您应该处理该列中非浮动的可能性：

import csv

mydelimeter = csv.excel()
mydelimeter.delimiter=";"
myfile = open("C:/Users/test/Documents/R_projects/homework/rdu-weather-history.csv")

# read the first line in the opened file ==> Header
myfile.readline()


myreader=csv.reader(myfile,mydelimeter)
mywind,mydate=[],[]
minTemp, maxTemp = [],[]
fastwindspeed, fog=[],[]

'''
create a variable that handle values of the 3 fields ==> Date - fastest5secwindspeed - fog
 and display the result where  
     fog ==> Yes    and highest speed  more than 10.
'''
for row in myreader:
    try:
        if row[11] =="Yes":
            if row[10] in (None, ""):
                raise Exception("this Record has empty value")
            try:
                if float(row[10]) < 10.0:
                    raise Exception( 'the wind speed  is below 10 mph in ' + row[0] )
            except ValueError:
                raise Exception('This Column expected to have a float has a non-float instead")

            print(row[0],row[10],row[11])
    except Exception as e:
        print("{}".format(e))

myfile.close()

Answer 2

我在项目工作期间也遇到过这个问题。我只是像下面这样：-

  if(len(row[10]) > 0):
      wind_speed = flot(row[10])