Python file IO http://chimera.labs.oreilly.com/books/1230000000393/ch05.html

0_io.py

# csv.py: csv file io
# file.py: operation related to files
# directory.py: operation related to finding files and traveling directory

csv.py

# http://chimera.labs.oreilly.com/books/1230000000393/ch06.html#_solution_94

#-----------------
# Read CSV
#-----------------
import csv
with open('stocks.csv') as f:
# or
with io.open(master_path + 'stock_mst.csv',encoding='cp932') as f:

  f_csv = csv.DictReader(f)
  for row in f_csv:
     # process row

#----------------

-
# Write CSV
#-----------------
headers = ['Symbol', 'Price', 'Date', 'Time', 'Change', 'Volume']
rows = [{'Symbol':'AA', 'Price':39.48, 'Date':'6/11/2007',
          'Time':'9:36am', 'Change':-0.18, 'Volume':181800},
        {'Symbol':'AIG', 'Price': 71.38, 'Date':'6/11/2007',
          'Time':'9:36am', 'Change':-0.15, 'Volume': 195500},
        ]

with open('stocks.csv','w') as f:
    f_csv = csv.DictWriter(f, headers)
    f_csv.writeheader()
    f_csv.writerows(rows)

directory.py

## listing files
from pathlib import Path
# current path
root_path = Path().resolve()

# file path
Path(__file__).parent.resolve()

#Listing subdirectories:
[x for x in p.iterdir() if x.is_dir()]

# python files
list(Path(path_string).glob('**/*.py'))

# Navigating 
p = Path('/etc')
q = p / 'init.d' / 'reboot' /'reboot.sh'
q.parent
q.parents # => list of parents

# path components
q.name # => filename
q.suffix # => extension 

# open text files.
p = Path('my_text_file')
p.write_text('Text file contents')
p.read_text()

# open general files:
with p.open() as f:
    f.readlines()

file.py

# Read the entire file as a single string
with open('rawdata.txt', 'r') as f:
  data = f.read()

# Iterate over the lines of the file
with open('somefile.txt', 'r') as f:
  for line in f:
    # process line
    ...

# write
f = open('out.txt', 'w')
f.write('aaa')
f.close()

# Write chunks of text data
with open('somefile.txt', 'wt') as f:
    f.write(text1)
    f.write(text2)
    ...

# Redirected print statement
with open('somefile.txt', 'wt') as f:
    print(line1, file=f)
    print(line2, file=f)

json.py

import json
with open('data/src/test.json') as f:
    df = json.load(f)


with open('data/src/test.json', 'w') as f:
  	# disable ensure ascii to avoid escaping. 
  	json.dump(df,f, ensure_ascii=False, indent=2)

pickle.py

import pickle

with open('singer.pickle', 'wb') as f:
    pickle.dump(singer, f)

with open('singer.pickle', 'rb') as f:
	obj = pickle.load(f)