如何解决此ValueError:无法将字符串转换为float？

Question

我要对所有列表对象执行数学运算：

swl = ['0', '0', '0', '', '', '', '1', '1', '1', '1', '1', '0.25']

数学运算：sgu = 1 - swl，我想把sgu格式化为：

sgu_compact = ['3*1', '3*', '5*0', '0.75']

这就是我所拥有的：

sgu = []
for ii in range(0, int(len(swl))):
    if len(swl[ii]) == 0:
        sgu.append(swl[ii])
    else:
        sgu.append(1-float(swl[ii]))

sguflt = [float(x) for x in swl]
sgu2 = ['{:g}'.format(float('{:.6g}'.format(i))) for i in sgu]

sgu_compact = ['%s*' % len(l) * (len(l) > 1) + k for k, g in groupby(sgu2)
                for l in (list(g),)]

print sgu_compact

但是我得到ValueError是因为空列表对象。有人能帮我吗？你知道吗

Answer 1

这可能是优化更多，但它似乎做什么你说你想要的。基本上，它只是检查并传递每个步骤中遇到的任何空字符串值。你知道吗

from itertools import groupby

swl = ['0', '0', '0', '', '', '', '1', '1', '1', '1', '1', '0.25']

sgu = []
for value in swl:
    if len(value):
        sgu.append(1 - float(value))
    else:
        sgu.append(value)

sguflt = [float(x) if x is not '' else '' for x in swl]

sgu2 = ['{:g}'.format(float('{:.6g}'.format(i))) if i is not '' else '' for i in sgu]

sgu_compact = ['%s*' % len(l) * (len(l) > 1) + k for k, g in groupby(sgu2)
                for l in (list(g),)]

print sgu_compact  # -> ['3*1', '3*', '5*0', '0.75']

Answer 2

只需过滤掉空值：

swl = ['0', '0', '0', '', '', '', '1', '1', '1', '1', '1', '0.25']
swl = [x for x in swl if len(x)]