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All this boring stuff is just begging to be automated in Python. By
programming your computer to do these tasks, you can transform it into
a quick-working file clerk who never makes mistakes.
As you begin working with files, you may find it helpful to be able
to quickly see what the extension (.txt, .pdf, .jpg, and so on) of a file is.
With OS X and Linux, your file browser most likely shows extensions
automatically. With Windows, file extensions may be hidden by default.
To show extensions, go to Start4Control Panel4Appearance and
Personalization4Folder Options. On the View tab, under Advanced
Settings, uncheck the Hide extensions for known file types checkbox.
the shutil module
The
shutil
(or shell utilities) module has functions to let you copy, move,
rename, and delete files in your Python programs. To use the
shutil
func-
tions, you will first need to use
import shutil
.
Copying Files and Folders
The
shutil
module provides functions for copying files, as well as entire folders.
Calling
shutil.copy(source, destination)
will copy the file at the path
source
to the folder at the path
destination
. (Both
source
and
destination
are
strings.) If
destination
is a filename, it will be used as the new name of the
copied file. This function returns a string of the path of the copied file.
Enter the following into the interactive shell to see how
shutil.copy()
works:
>>> import shutil, os
>>> os.chdir('C:\\')
u >>> shutil.copy('C:\\spam.txt', 'C:\\delicious')
'C:\\delicious\\spam.txt'
v >>> shutil.copy('eggs.txt', 'C:\\delicious\\eggs2.txt')
'C:\\delicious\\eggs2.txt'
The first
shutil.copy()
call copies the file at C:\spam.txt to the folder
C:\delicious. The return value is the path of the newly copied file. Note that
since a folder was specified as the destination u, the original spam.txt file-
name is used for the new, copied file’s filename. The second
shutil.copy()
call v also copies the file at C:\eggs.txt to the folder C:\delicious but gives
the copied file the name eggs2.txt.
While
shutil.copy()
will copy a single file,
shutil.copytree()
will
copy an entire folder and every folder and file contained in it. Call-
ing
shutil.copytree(source, destination)
will copy the folder at the path
source
, along with all of its files and subfolders, to the folder at the path
destination
. The
source
and
destination
parameters are both strings. The
function returns a string of the path of the copied folder.
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Enter the following into the interactive shell:
>>> import shutil, os
>>> os.chdir('C:\\')
>>> shutil.copytree('C:\\bacon', 'C:\\bacon_backup')
'C:\\bacon_backup'
The
shutil.copytree()
call creates a new folder named bacon_backup with
the same content as the original bacon folder. You have now safely backed up
your precious, precious bacon.
Moving and Renaming Files and Folders
Calling
shutil.move(source, destination)
will move the file or folder at the path
source
to the path
destination
and will return a string of the absolute path of
the new location.
If
destination
points to a folder, the
source
file gets moved into
destination
and keeps its current filename. For example, enter the following into the
interactive shell:
>>> import shutil
>>> shutil.move('C:\\bacon.txt', 'C:\\eggs')
'C:\\eggs\\bacon.txt'
Assuming a folder named eggs already exists in the C:\ directory, this
shutil.move()
calls says, “Move C:\bacon.txt into the folder C:\eggs.”
If there had been a bacon.txt file already in C:\eggs, it would have been
overwritten. Since it’s easy to accidentally overwrite files in this way, you
should take some care when using
move()
.
The
destination
path can also specify a filename. In the following
example, the
source
file is moved and renamed.
>>> shutil.move('C:\\bacon.txt', 'C:\\eggs\\new_bacon.txt')
'C:\\eggs\\new_bacon.txt'
This line says, “Move C:\bacon.txt into the folder C:\eggs, and while
you’re at it, rename that bacon.txt file to new_bacon.txt.”
Both of the previous examples worked under the assumption that there
was a folder eggs in the C:\ directory. But if there is no eggs folder, then
move()
will rename bacon.txt to a file named eggs.
>>> shutil.move('C:\\bacon.txt', 'C:\\eggs')
'C:\\eggs'
Here,
move()
can’t find a folder named eggs in the C:\ directory and so
assumes that
destination
must be specifying a filename, not a folder. So the
bacon.txt text file is renamed to eggs (a text file without the .txt file exten-
sion)—probably not what you wanted! This can be a tough-to-spot bug in
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your programs since the
move()
call can happily do something that might be
quite different from what you were expecting. This is yet another reason to
be careful when using
move()
.
Finally, the folders that make up the destination must already exist,
or else Python will throw an exception. Enter the following into the inter-
active shell:
>>> shutil.move('spam.txt', 'c:\\does_not_exist\\eggs\\ham')
Traceback (most recent call last):
File "C:\Python34\lib\shutil.py", line 521, in move
os.rename(src, real_dst)
FileNotFoundError: [WinError 3] The system cannot find the path specified:
'spam.txt' -> 'c:\\does_not_exist\\eggs\\ham'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "<pyshell#29>", line 1, in <module>
shutil.move('spam.txt', 'c:\\does_not_exist\\eggs\\ham')
File "C:\Python34\lib\shutil.py", line 533, in move
copy2(src, real_dst)
File "C:\Python34\lib\shutil.py", line 244, in copy2
copyfile(src, dst, follow_symlinks=follow_symlinks)
File "C:\Python34\lib\shutil.py", line 108, in copyfile
with open(dst, 'wb') as fdst:
FileNotFoundError: [Errno 2] No such file or directory: 'c:\\does_not_exist\\
eggs\\ham'
Python looks for eggs and ham inside the directory does_not_exist. It
doesn’t find the nonexistent directory, so it can’t move spam.txt to the path
you specified.
Permanently Deleting Files and Folders
You can delete a single file or a single empty folder with functions in the
os
module, whereas to delete a folder and all of its contents, you use the
shutil
module.
• Calling
os.unlink(path)
will delete the file at
path
.
• Calling
os.rmdir(path)
will delete the folder at
path
. This folder must be
empty of any files or folders.
• Calling
shutil.rmtree(path)
will remove the folder at
path
, and all files
and folders it contains will also be deleted.
Be careful when using these functions in your programs! It’s often a
good idea to first run your program with these calls commented out and
with
print()
calls added to show the files that would be deleted. Here is
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a Python program that was intended to delete files that have the .txt file
extension but has a typo (highlighted in bold) that causes it to delete .rxt
files instead:
import os
for filename in os.listdir():
if filename.endswith('.rxt'):
os.unlink(filename)
If you had any important files ending with .rxt, they would have been
accidentally, permanently deleted. Instead, you should have first run the
program like this:
import os
for filename in os.listdir():
if filename.endswith('.rxt'):
#os.unlink(filename)
print(filename)
Now the
os.unlink()
call is commented, so Python ignores it. Instead, you
will print the filename of the file that would have been deleted. Running
this version of the program first will show you that you’ve accidentally told
the program to delete .rxt files instead of .txt files.
Once you are certain the program works as intended, delete the
print(filename)
line and uncomment the
os.unlink(filename)
line. Then
run the program again to actually delete the files.
Safe Deletes with the send2trash Module
Since Python’s built-in
shutil.rmtree()
function irreversibly deletes files
and folders, it can be dangerous to use. A much better way to delete files and
folders is with the third-party
send2trash
module. You can install this module
by running
pip install send2trash
from a Terminal window. (See Appendix
A for a more in-depth explanation of how to install third-party modules.)
Using
send2trash
is much safer than Python’s regular delete functions,
because it will send folders and files to your computer’s trash or recycle bin
instead of permanently deleting them. If a bug in your program deletes
something with
send2trash
you didn’t intend to delete, you can later restore
it from the recycle bin.
After you have installed
send2trash
, enter the following into the interac-
tive shell:
>>> import send2trash
>>> baconFile = open('bacon.txt', 'a') # creates the file
>>> baconFile.write('Bacon is not a vegetable.')
25
>>> baconFile.close()
>>> send2trash.send2trash('bacon.txt')
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In general, you should always use the
send2trash.send2trash()
function
to delete files and folders. But while sending files to the recycle bin lets you
recover them later, it will not free up disk space like permanently deleting
them does. If you want your program to free up disk space, use the
os
and
shutil
functions for deleting files and folders. Note that the
send2trash()
function can only send files to the recycle bin; it cannot pull files out of it.
walking a directory tree
Say you want to rename every file in some folder and also every file in every
subfolder of that folder. That is, you want to walk through the directory tree,
touching each file as you go. Writing a program to do this could get tricky;
fortunately, Python provides a function to handle this process for you.
Let’s look at the C:\delicious folder with its contents, shown in Figure 9-1.
delicious
C:\
cats
catnames.txt
zophie.jpg
walnut
waffles
butter.txt
spam.txt
Figure 9-1: An example folder that
contains three folders and four files
Here is an example program that uses the
os.walk()
function on the
directory tree from Figure 9-1:
import os
for folderName, subfolders, filenames in os.walk('C:\\delicious'):
print('The current folder is ' + folderName)
for subfolder in subfolders:
print('SUBFOLDER OF ' + folderName + ': ' + subfolder)
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Organizing Files
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for filename in filenames:
print('FILE INSIDE ' + folderName + ': '+ filename)
print('')
The
os.walk()
function is passed a single string value: the path of a
folder. You can use
os.walk()
in a
for
loop statement to walk a directory
tree, much like how you can use the
range()
function to walk over a range of
numbers. Unlike
range()
, the
os.walk()
function will return three values on
each iteration through the loop:
1. A string of the current folder’s name
2. A list of strings of the folders in the current folder
3. A list of strings of the files in the current folder
(By current folder, I mean the folder for the current iteration of the
for
loop. The current working directory of the program is not changed by
os.walk()
.)
Just like you can choose the variable name
i
in the code
for i in
range(10):
, you can also choose the variable names for the three values
listed earlier. I usually use the names
foldername
,
subfolders
, and
filenames
.
When you run this program, it will output the following:
The current folder is C:\delicious
SUBFOLDER OF C:\delicious: cats
SUBFOLDER OF C:\delicious: walnut
FILE INSIDE C:\delicious: spam.txt
The current folder is C:\delicious\cats
FILE INSIDE C:\delicious\cats: catnames.txt
FILE INSIDE C:\delicious\cats: zophie.jpg
The current folder is C:\delicious\walnut
SUBFOLDER OF C:\delicious\walnut: waffles
The current folder is C:\delicious\walnut\waffles
FILE INSIDE C:\delicious\walnut\waffles: butter.txt.
Since
os.walk()
returns lists of strings for the
subfolder
and
filename
variables, you can use these lists in their own
for
loops. Replace the
print()
function calls with your own custom code. (Or if you don’t need one or
both of them, remove the
for
loops.)
compressing files with the zipfile module
You may be familiar with ZIP files (with the .zip file extension), which
can hold the compressed contents of many other files. Compressing a file
reduces its size, which is useful when transferring it over the Internet. And
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since a ZIP file can also contain multiple files and
subfolders, it’s a handy way to package several files
into one. This single file, called an archive file, can
then be, say, attached to an email.
Your Python programs can both create
and open (or extract) ZIP files using functions
in the
zipfile
module. Say you have a ZIP file
named example.zip that has the contents shown
in Figure 9-2.
You can download this ZIP file from http://
nostarch.com/automatestuff/ or just follow along
using a ZIP file already on your computer.
Reading ZIP Files
To read the contents of a ZIP file, first you must create a
ZipFile
object
(note the capital letters Z and F).
ZipFile
objects are conceptually similar
to the
File
objects you saw returned by the
open()
function in the previous
chapter: They are values through which the program interacts with the file.
To create a
ZipFile
object, call the
zipfile.ZipFile()
function, passing it a
string of the .zip file’s filename. Note that
zipfile
is the name of the Python
module, and
ZipFile()
is the name of the function.
For example, enter the following into the interactive shell:
>>> import zipfile, os
>>> os.chdir('C:\\') # move to the folder with example.zip
>>> exampleZip = zipfile.ZipFile('example.zip')
>>> exampleZip.namelist()
['spam.txt', 'cats/', 'cats/catnames.txt', 'cats/zophie.jpg']
>>> spamInfo = exampleZip.getinfo('spam.txt')
>>> spamInfo.file_size
13908
>>> spamInfo.compress_size
3828
u >>> 'Compressed file is %sx smaller!' % (round(spamInfo.file_size / spamInfo
.compress_size, 2))
'Compressed file is 3.63x smaller!'
>>> exampleZip.close()
A
ZipFile
object has a
namelist()
method that returns a list of strings
for all the files and folders contained in the ZIP file. These strings can be
passed to the
getinfo()
ZipFile
method to return a
ZipInfo
object about that
particular file.
ZipInfo
objects have their own attributes, such as
file_size
and
compress_size
in bytes, which hold integers of the original file size and
compressed file size, respectively. While a
ZipFile
object represents an entire
archive file, a
ZipInfo
object holds useful information about a single file in
the archive.
The command at u calculates how efficiently example.zip is compressed
by dividing the original file size by the compressed file size and prints this
information using a string formatted with
%s
.
cats
catnames.txt
zophie.jpg
spam.txt
Figure 9-2: The contents
of examplezip
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Extracting from ZIP Files
The
extractall()
method for
ZipFile
objects extracts all the files and folders
from a ZIP file into the current working directory.
>>> import zipfile, os
>>> os.chdir('C:\\') # move to the folder with example.zip
>>> exampleZip = zipfile.ZipFile('example.zip')
u >>> exampleZip.extractall()
>>> exampleZip.close()
After running this code, the contents of example.zip will be extracted
to C:\. Optionally, you can pass a folder name to
extractall()
to have it
extract the files into a folder other than the current working directory. If
the folder passed to the
extractall()
method does not exist, it will be created.
For instance, if you replaced the call at u with
exampleZip.extractall('C:\\
delicious')
, the code would extract the files from example.zip into a newly
created C:\delicious folder.
The
extract()
method for
ZipFile
objects will extract a single file from
the ZIP file. Continue the interactive shell example:
>>> exampleZip.extract('spam.txt')
'C:\\spam.txt'
>>> exampleZip.extract('spam.txt', 'C:\\some\\new\\folders')
'C:\\some\\new\\folders\\spam.txt'
>>> exampleZip.close()
The string you pass to
extract()
must match one of the strings in the
list returned by
namelist()
. Optionally, you can pass a second argument to
extract()
to extract the file into a folder other than the current working
directory. If this second argument is a folder that doesn’t yet exist, Python
will create the folder. The value that
extract()
returns is the absolute path
to which the file was extracted.
Creating and Adding to ZIP Files
To create your own compressed ZIP files, you must open the
ZipFile
object
in write mode by passing
'w'
as the second argument. (This is similar to
opening a text file in write mode by passing
'w'
to the
open()
function.)
When you pass a path to the
write()
method of a
ZipFile
object, Python
will compress the file at that path and add it into the ZIP file. The
write()
method’s first argument is a string of the filename to add. The second argu-
ment is the compression type parameter, which tells the computer what algo-
rithm it should use to compress the files; you can always just set this value to
zipfile.ZIP_DEFLATED
. (This specifies the deflate compression algorithm, which
works well on all types of data.) Enter the following into the interactive shell:
>>> import zipfile
>>> newZip = zipfile.ZipFile('new.zip', 'w')
>>> newZip.write('spam.txt', compress_type=zipfile.ZIP_DEFLATED)
>>> newZip.close()
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This code will create a new ZIP file named new.zip that has the com-
pressed contents of spam.txt.
Keep in mind that, just as with writing to files, write mode will erase
all existing contents of a ZIP file. If you want to simply add files to an exist-
ing ZIP file, pass
'a'
as the second argument to
zipfile.ZipFile()
to open
the ZIP file in append mode.
Project: renaming files with American-Style dates to
european-Style dates
Say your boss emails you thousands of files with American-style dates
(MM-DD-YYYY) in their names and needs them renamed to European-
style dates (DD-MM-YYYY). This boring task could take all day to do by
hand! Let’s write a program to do it instead.
Here’s what the program does:
• It searches all the filenames in the current working directory for
American-style dates.
• When one is found, it renames the file with the month and day swapped
to make it European-style.
This means the code will need to do the following:
• Create a regex that can identify the text pattern of American-style dates.
• Call
os.listdir()
to find all the files in the working directory.
• Loop over each filename, using the regex to check whether it has a date.
• If it has a date, rename the file with
shutil.move()
.
For this project, open a new file editor window and save your code as
renameDates.py.
Step 1: Create a Regex for American-Style Dates
The first part of the program will need to import the necessary modules
and create a regex that can identify MM-DD-YYYY dates. The to-do com-
ments will remind you what’s left to write in this program. Typing them as
TODO
makes them easy to find using IDLE’s
ctrl
-F find feature. Make your
code look like the following:
#! python3
# renameDates.py - Renames filenames with American MM-DD-YYYY date format
# to European DD-MM-YYYY.
u import shutil, os, re
# Create a regex that matches files with the American date format.
v datePattern = re.compile(r"""^(.*?) # all text before the date
((0|1)?\d)- # one or two digits for the month
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