我正在使用np.genfromtxt读取一个csv文件，并尝试使用converters参数来预处理每一列。
CSV：

"","Col1","Col2","Col3"
"1","Cell.1",NA,1
"2","Cell.2",NA,NA
"3","Cell.3",1,NA
"4","Cell.4",NA,NA
"5","Cell.5",NA,NA
"6","Cell.6",1,NA

代码：

import numpy as np

filename = 'b.csv'
h = ("", "Col1", "Col2", "Col3")

def col1_converter(v):
    print(f'col1_converter {v = }')
    return v

def col2_converter(v):
    print(f'col2_converter {v = }')
    return v

def col3_converter(v):
    print(f'col3_converter {v = }')
    return v

a = np.genfromtxt(
    filename,
    delimiter=',',
    names=True,
    dtype=[None, np.dtype('U8'), np.dtype('U2'), np.dtype('U2')],
    usecols=range(1, len(h)),
    converters={1: col1_converter, 2: col2_converter, 3: col3_converter},
    deletechars='',
)
print()
print(a)

当我在转换器中输入print语句时，我看到在开始时打印了一个无关的1行，它实际上并没有出现在输出的矩阵中。为什么我会看到这一行1？

col1_converter v = b'1'
col2_converter v = b'1'
col3_converter v = b'1'
col1_converter v = b'"Cell.1"'
col1_converter v = b'"Cell.2"'
col1_converter v = b'"Cell.3"'
col1_converter v = b'"Cell.4"'
col1_converter v = b'"Cell.5"'
col1_converter v = b'"Cell.6"'
col2_converter v = b'NA'
col2_converter v = b'NA'
col2_converter v = b'1'
col2_converter v = b'NA'
col2_converter v = b'NA'
col2_converter v = b'1'
col3_converter v = b'1'
col3_converter v = b'NA'
col3_converter v = b'NA'
col3_converter v = b'NA'
col3_converter v = b'NA'
col3_converter v = b'NA'

[('"Cell.1"', 'NA', '1') ('"Cell.2"', 'NA', 'NA') ('"Cell.3"', '1', 'NA')
 ('"Cell.4"', 'NA', 'NA') ('"Cell.5"', 'NA', 'NA') ('"Cell.6"', '1', 'NA')]