'builtin_function_or_method' to list

Question

I understand the fact that Python is a dynamic language, but the below code is bothering me.

I have the below simple program , which has some helper function to wrap command execution.

EventLoaderToVerticaHelper is a helper class with two methods, so when I call "get_filenames_from_hdfs_with_filter" it should throw an error or return a list of String.

class EventLoaderToVerticaHelper:
    def __init__(self):
        pass

    @staticmethod
    def execute_command(cmd):
        p = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
        error_lines = p.stderr.readlines()
        if len(error_lines) > 0:
            raise error_lines
        return p.stdout.readlines

    @staticmethod
    def get_filenames_from_hdfs_with_filter(folder, filetype):
        cmd = "hdfs dfs -ls {0}/*.{1} |  awk '{print $8}'".replace("{0}", folder).replace("{1}", filetype)
        return EventLoaderToVerticaHelper.execute_command(cmd)

The below code uses the above helper,

from src.EventLoaderToVerticaHelper import EventLoaderToVerticaHelper
if __name__ == '__main__':
     filelist = EventLoaderToVerticaHelper.get_filenames_from_hdfs_with_filter("/user/cloudera/testfiles", "csv")
     for s in filelist:
        print s

When I run the above program I get below error. I'm sure that return type if List[Str]

Traceback (most recent call last):
  File "/home/cloudera/PycharmProjects/vertical-event-loader/src/EventLoaderToVertica.py", line 29, in <module>
for s in filelist:
TypeError: 'builtin_function_or_method' object is not iterable

I know that I'm expecting it to behave kind of a Typed language ... I want to method to return List[Str], when there is a exception I want to terminate the program.

How can I achieve this, I tried with return type and other things but no luck.

You are returning the method `readlines` (`return p.stdout.readlines`), you aren't calling it. — Dimitris Fasarakis Hilliard, Aug 22 '17 at 15:40
Jim Fasarakis Hilliard you answered the question first, how can mark your comment as answer ? — Dave, Aug 22 '17 at 15:44
Also, what do your expect `raise error_lines` to do? The (first) argument to `raise` should be an exception object. — PM 2Ring, Aug 22 '17 at 15:44
Checking for output to standard error isn't a good way to determine if a command succeeds. A command can fail without writing to standard error, and it can write diagnostic information while succeeding. — chepner, Aug 22 '17 at 15:45
A class with no state and two static methods shouldn't be a class - it should be two module-level functions... — juanpa.arrivillaga, Aug 22 '17 at 15:50
will check the output as well https://stackoverflow.com/questions/23420990/subprocess-check-output-return-code .. @chepner — Dave, Aug 22 '17 at 15:56

score 5 · Answer 1 · answered Aug 22 '17 at 15:42

5

return p.stdout.readlines

Should be instead

return p.stdout.readlines()

Note that you did call the readlines correctly two lines above, when you read from stderr.

answered Aug 22 '17 at 15:42

moshez

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'builtin_function_or_method' to list

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