13.1 Opening files

file_object = open('myfile', 'r')
line = file_object.readline():

import os
file_name = os.path.join("c:", "My Documents", "test", "myfile")
file_object = open(file_name,'r')

13.2 Closing files

file_object = open("myfile", 'r')
line = file_object.readline()
# . . . any further reading on the file_object . . .
file_object.close()

13.2 Opening files in other modes

file_object = open("myfile", 'w')
file_object.write(“Hello, World\n”)
file_object.close()

13.4 Read and write text or binary data

file_object = open("myfile", 'r')
count = 0
while file_object.readline() != "":
    count = count + 1
print(count)
file_object.close()

file_object = open("myfile", 'r')
print(len(file_object.readlines()))
file_object.close()

file_object = open("myfile", 'r')
count = 0
for line in file_object:
    count = count + 1
print(count)
file_object.close()

# Open a file for reading.
input_file = open("myfile", newline="\n")

inpu_filet = open("myfile.txt", 'r')
lines = input_file.readlines()
input_file.close()
output = open("myfile2.txt", 'w')
output.writelines(lines)
output.close()

# Open a file for reading in binary mode.
input_file = open("myfile", 'rb')
# Read the first four bytes as a header string.
header = input_file.read(4)
# Read the rest of the file as a single piece of data.
data = input_file.read()
input.close()

13.5 Screen input/output

>>> x = input("enter file name to use: ")
enter file name to use: myfile
>>> x
'myfile'

>>> x = int(input("enter your number: "))
enter your number: 39
>>> x
39

>>> import sys
>>> print("Write to the standard output.")
Write to the standard output.
>>> sys.stdout.write("Write to the standard output.\n")
Write to the standard output.
30
>>> s = sys.stdin.readline()
An input line
>>> s
'An input line\n'

>>> import sys
>>> f= open("outFile.txt",'w')
>>> sys.stdout = f
>>> sys.stdout.writelines(["A first line.\n","A seconde line.\n"])
>>> print("A line from the print statement")
>>> 3+4
>>> sys.stdout = sys.__stdout__
>>> f.close()
>>> 3+4
7
>>> import sys
>>> f= open("outFile.txt",'w')
>>> print("A first line.","A seconde line.", file=f)
>>> 3+4
7
>>> f.close()
>>> 3+4
7

13.6 struct module

import struct
    record_format = 'hd4s'
    record_size = struct.calcsize(record_format)
    result_list = []
    input = open("data", 'rb')
    while 1:
        # Read in a single record.
        record = input.read(record_size)
        # If the record is empty, it indicates we have reached the end of file, so quit the loop.
        # Note that we have made no provision for checking for file consistency,
        # i.e. that the file contains a number of bytes which is an integer multiple
        # of the record size. However, if the last record is an "odd" size, the
        # struct.unpack function will raise an error.
        if record == '': 
            input.close()
            break
        # Unpack the record into a tuple, and append that tuple to the result list.
        result_list.append(struct.unpack(record_format, record))

>>> import struct
>>> record_format = 'hd4s'
>>> struct.pack(record_format, 7, 3.14, 'gbye')
b'\x07\x00\x00\x00\x1f\x85\xebQ\xb8\x1e\t@gbye'

13.7 pickling

>>> import pickle
>>> file = open("solecache",'w')
>>> pickle.dump({}, file)
>>> file.close()

13.8 Shelving

>>> import shelve
>>> book = shelve.open("addresses")

>>> book['flintstone'] = ('fred', '555-1234', '1233 Bedrock Place')
>>> book['rubble'] = ('barney', '555-4321', '1235 Bedrock Place') 

>>> book..close()

>>> import shelve
>>> book = shelve.open("addresses")

>>> book['flintstone']
('fred', '555-1234', '1233 Bedrock Place')