Python: Part3 - Files

1.Filenames and Absolute/Relative paths:

'c:\\spam\\eggs.png'

'c:\\spam\\eggs.png'

print('\\')

\

r'c:\spam\eggs.png'

'c:\spam\eggs.png'

1.1 Importing os

import os
os.path.join('folder1','folder2','folder3','file.png')

'folder1\\folder2\\folder3\\file.png'

os.sep

'\\'

os.getcwd()  # get current working directory

os.chdir('c:\\')
os.getcwd()
os.chdir('C:\\ProgramData\\Microsoft\\Windows\\Start Menu\\Programs\\Python 3.5')
os.path.abspath('spam.png')
'C:\\ProgramData\\Microsoft\\Windows\\Start Menu\\Programs\\Python 3.5\\spam.png'

1.2 os.path.isabs() , os.path.relpath()

os.path.isbs('..\\..\\spam.png') 

False

os.path.isabs('C:\\folder\\folder')

True

os.path.relpath('c:\\folder1\\folder2\\spam.png','c:\\folder1')

'folder2\\spam.png'

os.path.dirname('c:\\folder1\\folder2\\spam.png')

'c:\\folder1\\folder2'

os.path.basename('c:\\folder1\\folder2\\spam.png')

'spam.png'

os.path.basename('c:\\folder1\\folder2')

folder2

1.3 os.path.isfile() , os.path.isdir()

os.path.exists('c:\\folder1\\folder2')

False

os.path.exists('c:\\windows\\system32\\calc.exe')

True

os.path.isfile('c:\\windows\\system32\\calc.exe')

True

os.path.isfile('c:\\windows\\system32')

False

os.path.isdir('c:\\windows\\system32')

True

os.path.isdir('c:\\windows\\seenu')

False

1.4 os.path.getsize()

os.path.getsize('c:\\windows\\system32\\calc.exe')

918528

list the files inside a directory

os.listdir('c:\\srinivas')

total size of the files inside the folder

 for filename in os.listdir('c:\\srinivas')
     if not os.path.isfile(os.path.join('c:\\srinivas',filename)):
           continue
     totalsize = totalsize + os.path.getsize(os.path.join('c:\\srinivas',filename))

totalsize

1.5 os.makedirs()

os.makedirs('c:\\srinvas\\folder1\\folder2')

Recap :

• Files have a name and a path.
• The root folder is the lowest folder.
• In a file path, the folders and filename are separated by backslashes on Windows and forward slashes on Linux and Mac.
• Use the os.path.join() function to combine folders with the correct slash.
• os.getcwd() will return the current working directory.
• os.chdir() will change the current working directory.
• Absolute paths begin with the root folder, relative paths do not.
• The . folder represents "this folder", the .. folder represents "the parent folder".
• os.path.abspath() returns an absolute path form of the path passed to it.
• os.path.relpath() returns the relative path between two paths passed to it.
• os.makedirs() can make folders.
• os.path.getsize() returns a file's size.
• os.listdir() returns a list of strings of filenames.
• os.path.exists() returns True if the filename passed to it exists.
• os.path.isfile() and os.path.isdir() return True if they were passed a filename or file path.

2.Reading and Writing Plain Text Files

create a file hellworld.txt with content

#helloworld.txt

Hello World!
How are you?

helloFile = open('C:\srinivas\hellworld.txt') # it opens the files in readonly mode
helloFile.read()

'Hello World!\nHow are you?'

helloFile.close()

helloFile = open('C:\srinivas\hellworld.txt')
content=helloFile.read()
print(content)

Hello World!
How are you?'


helloFile.close()

2.1 readlines() Method - It returns the list of strings

helloFile = open('C:\srinivas\hellworld.txt')
helloFile.readlines()

['Hello world!\n','How are you?']


helloFile.close()

2.2 Write Mode - It overrides the existing with new values
pass the second parameter to the open as 'w'

helloFile = open('C:\srinivas\hello2.txt','w') # if the file does not exists it will create one
helloFile.write('Hello!!!!!')

12 ###### writes the number of bytes it has written

helloFile.write('Hello!!!!!')

12

helloFile.write('Hello!!!!!')

12

helloFile.close()

helloFile.write('Hello!!!!!\n')

appleFile=open('apple.txt','w')
appleFile.write('Apple is not a vegetable.')
appleFile.close()
import os
os.getcwd()

appleFile = open('apple.txt','a')
appleFile.write('\n\nApple milkshake is declicious.')

appleFile.close()

2.3 shelve module can store Python values in a binary file

import shelve
shelfFile = shelve.open['mydata']
shelfFile['cats']=['zophie','Pooka','Simon','cleo']
shelfFile.close()

#check the current working directory, it will create 3 files
mydata.bak ,mydata.dat, mydata.dir


shelfFile = shelve.open('mydata')
shelfFile['cats']

shelfFile = shelve.open('mydata')

list(shelfFile.keys())




list(shelfFile.values())

mydata.bak
mydata.dat
mydata.dir

2.4 Append Mode: Appends the content to the txt file

helloFile = open('C:\srinivas\hellworld.txt','a')

Recap :

• The open() function will return a file object which has reading and writing –related methods.
• Pass ‘r' (or nothing) to open() to open the file in read mode. Pass ‘w' for write mode. Pass ‘a' for append mode.
• Opening a nonexistent filename in write or append mode will create that file.
• Call read() or write() to read the contents of a file or write a string to a file.
• Call readlines() to return a list of strings of the file's content.
• Call close() when you are done with the file.
• The shelve module can store Python values in a binary file.
• The shelve.open() function returns a dictionary-like shelf value.

3. Copying and Moving Files and Folders

• To work with copying and moving files and folders ,import shutil module

import shutil

shutil.copy('c:\\spam.txt','c:\srinivas')
#copy and rename the file
shutil.copy('c:\\spam.txt','c:\srinivas\spammodified.txt')
#copy entire folders and files
shutil.copytree('c:\delicious',c:\delicious_backup')
#output :'c:\delicious_backup'

#if wanted to move a file to a new location
shutil.move('c:\\spam.txt','c:\\delicious\\walnut')
#output : 'c:\delicious\walnut\spam.txt'

# there is nothing like shutil.rename, instead try the below one

shutil.move('c:\\delicious\\walnut\\spam.txt','c:\\delicious\\walnut\\eggs.txt'

4. Deleting the files

4.1 os.unlink() - to delete a file

import os
os.getcwd()
os.unlink('bacon.txt') 

4.2 os.rmdir() -if any file exists in a folder and it will fail

os.rmdir('c:\\delicious')

it will fail if files existing in the folder

4.3 shutil.rmtree() => Deletes a folder and its entire contents.

import shutil
shutil.rmtree('c:\\delicious')

4.3.1 Dry Run

import os
os.chdir('C:\\Users\\Srini\\Desktop')

for filename in os.listdir() :
   if filename.endswith('.txt'):
        #os.unlink(filename)
        print(filename)

4.4 sendtotrash module()

we need to install using pip

cd "c:\Program Files\Python 3.5\Scripts\

c:\Program Files\Python 3.5\Scripts> pip.exe install send2trash

import send2trash
send2trash.send2trash('c:\\users\srini\\desktop\\IMPORTANT_FILE!!!!.rxt'

it will delete the file and moves to trash

Recap:

• os.unlink() will delete a file.
• os.rmdir() will delete a folder (but the folder must be empty).
• shutil.rmtree() will delete a folder and all its contents.
• Deleting can be dangerous, so do a "dry run" first.
• send2trash.send2trash() will send a file or folder to the recycling bin.

Conclusion : Discussed about python - dictionaries used IDLE shell command for running the python code

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