File Management in Python

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File management is a basic function, and an important part of many applications. Python makes file management surprisingly easy, especially when compared

Reading and Writing

open a file for writing:
fileHandle = open ( 'test.txt', 'w' )

The next step is to write data to the file:
fileHandle.write ( 'This is a test.nReally, it is.' )

Finally, we need to clean up after ourselves and close the file:
fileHandle.close()

To get past this, use the "a" mode to append data to a file, adding data to the bottom:

fileHandle = open ( 'test.txt', 'a' )
fileHandle.write ( 'nnnBottom line.' )
fileHandle.close()

Read a file
Now let's read our file and display the contents:

- read the entire file and print the data within it.

fileHandle = open ( 'test.txt' )
print fileHandle.read()
fileHandle.close()

- read a single line in the file:
fileHandle = open ( 'test.txt' )
print fileHandle.readline() # "This is a test."
fileHandle.close()

- store the lines of a file into a list:

fileHandle = open ( 'test.txt' )
fileList = fileHandle.readlines()
for fileLine in fileList:
print '>>', fileLine
fileHandle.close()

Adjust Offset

When reading a file, Python's place in the file will be remembered, illustrated in this example:

fileHandle = open ( 'test.txt' )
garbage = fileHandle.readline()
fileHandle.readline() # "Really, it is."
fileHandle.close()

Only the second line is displayed. We can, however, get past this by telling Python to resume reading from a different position:

fileHandle = open ( 'test.txt' )
garbage = fileHandle.readline()
fileHandle.seek ( 0 )
print fileHandle.readline() # "This is a test."
fileHandle.close()

In the above example, we tell Python to continue reading from the first byte in the file.
Thus, the first line is printed. We can also request Python's place within the file:

fileHandle = open ( 'test.txt' )
print fileHandle.readline() # "This is a test."
print fileHandle.tell() # "17" current offset
print fileHandle.readline() # "Really, it is."

It is also possible to read the file a few bytes at a time:

fileHandle = open ( 'test.txt' )
print fileHandle.read ( 1 ) # "T"
fileHandle.seek ( 4 )
print FileHandle.read ( 1 ) # "T"

Binary Mode

read and write files in binary mode, such as images or executional files.
To do this, simply append "b" to the file mode:

fileHandle = open ( 'testBinary.txt', 'wb' )
fileHandle.write ( 'There is no spoon.' )
fileHandle.close()

fileHandle = open ( 'testBinary.txt', 'rb' )
print fileHandle.read()
fileHandle.close()