Python-based File Operation

A Python-based File Operation is a file operation that is a Python operation.

• Context:
  • It can range from being a Python File Open Operation to being a Python File Close Operation (on Python file descriptors).
  • It can range from being a Python File Read Operation to being a Python File Write Operation (such as a Python file append operation).
  • It can range from being a Python File Metadata Operation.
• Example(s):
  • with open('testit.txt', encoding="utf8") as f:
      inputFileText = f.read()
      mylist = f.read().splitlines()
print(inputFileText)
mylist[0:10]
  • infile = open('file.csv', encoding="utf8")
data_list = [line.rstrip().split(',') for line in infile.readlines()]
  • allFiles = glob.glob("./*.csv.zip")
  • a Pandas-based File Operation, such as:
    • df = pandas.read_csv("./file.csv.zip", compression='zip', header=0, sep=',', quotechar='"', skiprows=0) ;
    • pandas_df.to_csv("out.tsv", sep='\t', index=True, cols=["col3","col1"], encoding='utf-8') ;
  • …
• Counter-Example(s):
  • Scala File Operation, R File Operation, Perl File Operation, Hive File Operation, ...
  • a Python Data Management Operation (e.g. sampling), ...
  • a Python Data Conversion Operation.
• See: Python Coding Example.

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References

• https://docs.python.org/2/tutorial/inputoutput.html

2014

• http://en.wikibooks.org/wiki/Python_Programming/Files
  • Files, specifically file handles, are an important example of resources, and thus should generally be managed using the with statement; see context managers section.

    In rare cases – namely when a file is not only used within a single block of code – it is necessary to do manual resource management using File.close(), but this is error-prone and requires great care to be exception safe. In interactive use using explicit open() and File.close() results in immediate evaluation, instead of the delayed evaluation of using a with statement.

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Examples

Reading & Writing Files

Just reading from a file

 open my $io, "<-" or die "NO STDIN: $!" ;

Mixed Read & Write

...

Subroutine-based

Subroutine to open a file for writing and write into it.

import csv
filename = sys.argv[1]
with open(filename, 'rb') if sys.argv[1] is not "-" else sys.stdin as f:
   reader = csv.reader(f,dialect="excel-tab")  # creates the reader object
   for row in reader:
      ...

Subroutine to open a file for writing and write into it.

...

File Open Codes

...

File Management

Rename a File

...

Delete a file

...

Choose between STDIN or file

...

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Directory-based operations

Read a directory's files (shortcut with pattern matching).

...

Load all files in a directory into the @files array

...

a subroutine approach

...

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JSON-based operations

import json

with open("data_file.json", "w") as write_file:
    json.dump(data, write_file)

print(json.dumps({'4': 5, '6': 7}, sort_keys=True, indent=4))
 {
    "4": 5,
    "6": 7
 }

...

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