从命令行输入初始化Python对象

Question

I'm new to Python and am learning input/output. Right now, I'm trying to add attributes to an object from a file that I specify from command line input.

For example, I want to run the following: $ /...filepath.../ python3 myCode.py < 06 to pass the contents of file 06

$ /...filepath.../ cat 06
7
4 5 2 7 88 2 1

to myCode.py . Both myCode.py and 06 are located in the same directory.

I'm trying to create a MyClass object from a command line call with attributes to be as follows:

## myCode.py ##

# create class
class MyClass(object):
    def __init__(self):
    self._num_one = int(sys.stdin.readline())    
    self._num_many = [int(x) for x in sys.stdin.readline().split()]

# print attributes
print(MyClass()._num_many)
print(MyClass()._num_one)

but I'm getting the following error ValueError: invalid literal for int() with base 10: '' for self._num_one but am able tor print self._num_many and am not sure why. If I swap the order of self._num_one and self.num_many , then I can get self._num_one . Since 06 is only two lines long, is there a first line that I'm not initially reading? Why can I only print one of the two attributes, and how would I print both?

Many thanks.

Answer 1

just because your input stream is not an int, it's a string with space and "\\n" delimiter, you have to work on these things first.

The quick and easy way is changing your code to something like this (not tested):

self._num_one = int("".join(sys.stdin.readline().split()))

Answer 2

There are some problems with your code that stops it from working.

First thing first, you need to remove whitespace before and after if you are reading the input file one line after another. This means a call to the .strip() method after .readline() . You are getting the ValueError because int() cannot process non-numeric string.

>>> int('x')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 10: 'x'
>>> int(' ')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 10: ' '
>>> int('\n')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 10: '\n'
>>> int('1')
1

So the code becomes

class MyClass(object):
    def __init__(self):
        self._num_one = int(sys.stdin.readline().strip())
        self._num_many = [int(x) for x in sys.stdin.readline().strip().split()]

Secondly, whenever you do MyClass() it instantiates a new object. If I understand the code correctly, it is expecting to read two lines twice (4 lines in total). Given the input file, I am assuming you are interested in instantiating ONE object. Therefore we instantiate one, and tag it to a variable, then use that reference later.

instantiatedObject = MyClass()
print(instantiatedObject._num_many)
print(instantiatedObject._num_one)