title: IOError: [Errno 2] No such file or directory trying to open a file in python
body: <p>I  am new to Python so please forgive the following basic code and problem, but I have been trying to figure out what is causing the error I am getting.</p>
  
  <p>Here is what I am trying to do:</p>
  
  <ol>
  <li>loop through a specific folder</li>
  <li>iterate each csv files in that specific folder</li>
  <li>perform calculations</li>
  </ol>
  
  <p>Here is my code:</p>
  
  <pre>    import os
      import csv
  
      def get_all_files(directory):
          dir_list = os.listdir(directory)
          csv_files = []
          for e in dir_list:
              if e.endswith('.csv'):
                 csv_files.append(e)
           return csv_files
  
      def sum_from_csv(csv_file):
          cr = csv.reader(open(csv_file, 'r'))
          cr.next()
          file_content=cr.readlines()
  
          #initialize throughput total as zero
          throughput_total=0
          #array to save throughput in every iteration
          throughput_dataset=[]
  
          for line in file_content:
            line=line.strip()
            data=line.split(",")[1]
            float_data=float(data)
            throughput_total+=float_data
            throughput_dataset.append(float_data)
          #to calculate number of dataset
          dataset_length=len(throughput_dataset)
          throughput_average=throughput_total/dataset_length
          throughput.append(throughput_average)
          print "Throughput-total is",throughput_total
          print "Average is",throughput_average
  
     csv_files = get_all_files('/home/gwthamy/Desktop/MyProject/siddhi-benchmarks/filter-4.0.0-M20/filtered-results-filter-4.0.0-M20')
  
     for each in csv_files:
          sum_from_csv(each)</pre>
  
  <p>Here is the error I am getting:</p>
  
  <pre>    IOError: [Errno 2] No such file or directory: 'output-0-1502441456439.csv'</pre>
  
  <p>I have confirmed that the folder and file do exist. What is causing the IOError and how to I resolve it? Also, is there anything else wrong with my code that would prevent me from performing the entire task?</p>
  
  <p>Thanks in advance </p>