从命令行读取 (x, y) 对流并将修改后的对 (x, f(y)) 写入文件

Question

这是问题所在：

从命令行读取 (x, y) 对流。修改 datatrans1.py 脚本，使其从命令行读取 (x, y) 对流并将修改后的对 (x, f(y)) 写入文件。新脚本的用法，这里叫做datatrans1b.py，应该是这样的：

这是命令行的输入：
python datatrans1b.py tmp.out 1.1 3 2.6 8.3 7 -0.1675

生成输出文件 tmp.out:

1.1 1.20983e+01
2.6 9.78918e+00
7 0.00000e+00

提示：运行通过for循环中的sys.argv数组并使用range函数具有适当的起始索引和增量以下是datatrans1.py原稿：

```
import sys, math

try:
   infilename = sys.argv[1]
   outfilename = sys.argv[2]
except:
   print("Usage:", sys.argv[0], "infile outfile")
   sys.exit(1)

ifile = open(infilename, 'r')  # open file for reading
ofile = open(outfilename, 'w')  # open file for writing


def myfunc(y):
   if y >= 0.0:
       return y ** 5 * math.exp(-y)
   else:
       return 0.0

```

逐行读取 ifile 并写出转换后的值：

```

for line in ifile:
   pair = line.split()
   x = float(pair[0])
   y = float(pair[1])
   fy = myfunc(y)  # transform y value
   ofile.write('hello' '%g  %12.5e\n' % (x, fy))
ifile.close()
ofile.close()

```

关于如何修改上述代码以正确运行命令行参数并生成具有坐标对的 tmp.out 文件的任何线索都将非常有用

Answer 1

这应该可以解决问题：

import sys, math

try:
   outfilename = sys.argv[1]
except:
   print("Usage:", sys.argv[0], "outfile pairs")
   sys.exit(1)

ofile = open(outfilename, 'w')  # open file for writing

def myfunc(y):
   if y >= 0.0:
       return y ** 5 * math.exp(-y)
   else:
       return 0.0

# Loop through y values, using slices to start at position 3
# and get every second value
for i, y in enumerate(sys.argv[3::2]):

    # The corresponding x value is the one before the selected y value
    x = sys.argv[2:][i*2]

    # Call myfunc with y, converting y from string to float.
    fy = myfunc(float(y))

    # Write output using f-strings
    ofile.write(f'({x}, {fy})\n')

从命令行读取 (x, y) 对流并将修改后的对 (x, f(y)) 写入文件

reads a stream of (x, y) pairs from the command line and writes the modified pairs (x, f(y)) to a file

python

command-line

file

coordinates

argv