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Aya Bouchiha
Aya Bouchiha

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Understanding 11 Important Python File Handling Methods

#python #beginners #codenewbie #programming

Hi, I'm Aya Bouchiha, today, we'll talk about 11 important python file handling methods.

close

  • close(): helps you to close an opened file. 
test_file = open('test.txt', 'r') first_line = test_file.readline() # do something...  test_file.close()
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There is another method to close a file, that works automaticly without using close method:

with open('test.txt', 'r') as test_file: first_line = test_file.readline() # do something
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readable

  • readable(): checks if a specified file is readable. 
with open('test.txt', 'w') as test_file: print(test_file.readable()) # False  print(test_file.readline()) # error  with open('test.txt', 'r') as test_file: print(test_file.readable()) # True
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read

  • read(size= -1): returns the given number of bytes (by default -1) from a specified file.

test.txt

Hello, I'm Aya Bouchiha This is an Example Aya Bouchiha Test
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index.py

with open('test.txt', 'r') as test_file: print(test_file.read(28)) # Hello, I'm Aya Bouchiha  # This  print(test_file.read()) # is an Example  # Aya Bouchiha  # Test  print(test_file.read()) # ""
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readline

  • readline(size=-1): used to read a given number of bytes (by default = -1) in a line from a specified file.

test.text:

Hello, I'm Aya Bouchiha This is an Example Aya Bouchiha Test
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index.py:

with open('test.txt', 'r') as test_file: first_line = test_file.readline() second_line = test_file.readline() fname_from_third_line = test_file.readline(3) print(first_line) # Hello, I'm Aya Bouchiha  print(second_line) # This is an Example  print(fname_from_third_line) # Aya
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readlines

  • readlines(N = -1): returns all file lines as a list. N parameter is used to limit the number of lines returned. If the total number of bytes returned exceeds the specified number, no more lines are returned.

for more details:

user.txt:

Aya Bouchiha developer.aya.b@gmail.com https://t.me/AyaBouchiha
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index.py:

with open('user.txt', 'r') as user_file: # [  # "Aya Bouchiha\n",  # "developer.aya.b@gmail.com\n",  # "https://t.me/AyaBouchiha\n",  # ]  print(user_file.readlines()) user_file.seek(0) print(user_file.readlines(3)) # ["Aya Bouchiha\n"]
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seek, tell

  • seek(pos): helps you to specifiy the cursor's position, and gets the new one. more details

  • tell(): lets you get the file's current position.

test.text:

Hello, I'm Aya Bouchiha This is an Example Aya Bouchiha Test
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index.py:

with open('test.txt', 'r') as test_file: print(test_file.tell()) # 0  first_line = test_file.readline() # Hello, I'm Aya Bouchiha  current_position = test_file.seek(7) # "hello, " is ignored, len("hello, ") is 7  print(current_position) # 7  print(test_file.tell()) # 7  print(test_file.read()) # I'm Aya Bouchiha  # This is an Example  # Aya Bouchiha  # Test
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writable

  • writable(): checks if the specified file is writable. 
with open('test.txt', 'r') as test_file: print(test_file.readable()) # True  print(test_file.writable()) # False  with open('test.txt', 'w+') as test_file: print(test_file.readable()) # True  print(test_file.writable()) # True
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write

  • write(value): lets you write a given value in a specified file.

message.txt:

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index.py:

with open('message.txt', 'w') as message_file: message = 'Good morning!' message_file.write(message)
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message.txt:

Good morning!
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writelines

  • writelines(sequence): used to write a sequence of items in a specified file.more details

Example 1:

emails.txt:

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index.py:

emails = ["developer.aya.b@gmail.com\n", "john.doe@gmail.com",] with open('emails.txt', 'w') as emails_file: emails_file.writelines(emails)
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emails.txt:

developer.aya.b@gmail.com john.doe@gmail.com
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Example 2:

admins.txt:

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index.py:

admins = ["Aya Bouchiha\n", "John Doe\n", "Simon Spouf"] with open('admins.txt', 'a+') as admins_file: print(admins_file.readable()) # True  print(admins_file.writable()) # Trye  admins_file.write("Hi, welcome to admins.txt\n") admins_file.write('admins are:\n') admins_file.writelines(admins) print(admins_file.tell()) # 75  admins_file.seek(0) print(admins_file.read()) # Hi, welcome to admins.txt  # admins are:  # Aya Bouchiha  # John Doe  # Simon Spouf
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admins.txt:

Hi, welcome to admins.txt admins are: Aya Bouchiha John Doe Simon Spouf
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truncate

  • truncate(size): lets you truncate the file size.

Example 1:

emails.txt:

developer.aya.b@gmail.com john.doe@gmail.com
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with open('emails.txt', 'a+') as emails_file: email_address = 'developer.aya.b@gmail.com' emails_file.truncate(len(email_address)) emails_file.seek(0) # developer.aya.b@gmail.com  print(emails_file.read())
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emails.txt:

developer.aya.b@gmail.com
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Example 2:

emails.txt:

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index.py:

with open('emails.txt', 'a+') as emails_file: emails = [ "developer.aya.b@gmail.com\n", "john.doe@gmail.com\n", "someone.d@gmail.com" ] emails_file.writelines(emails) emails_file.seek(0) # developer.aya.b@gmail.com  print(emails_file.readline()) emails_file.truncate(len("".join(emails[:2]))) emails_file.seek(0) # developer.aya.b@gmail.com  # john.doe@gmail.com  print(emails_file.read()) emails_file.seek(len(emails[0])) # size = cursor's position which is len(emails[0])  emails_file.truncate() # 26  print(emails_file.tell()) emails_file.seek(0) # developer.aya.b@gmail.com  print(emails_file.read())
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emails.txt:

developer.aya.b@gmail.com
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Summary

  • close(): closes an opened file.
  • readable(): checks if a specified file is readable.
  • read(size= -1): returns the given number of bytes (by default -1) from a specified file.
  • readline(size=-1): reads a given number of bytes (by default = -1) in a line from a specified file.
  • readlines(N = -1): returns all file lines as a list.
  • seek(pos): specifiy the cursor's position, and returns the new one.
  • tell(): returns the file's current position.
  • writable(): checks if the specified file is writable.
  • write(value): writes a given value in a specified file.
  • writelines(sequence): writes a sequence of items in a specified file.
  • truncate(size): truncates the file size.

References & Useful Resources

Articles

Youtube Videos

Suggested Posts

To Contact Me:

email: developer.aya.b@gmail.com

telegram: Aya Bouchiha

Hope you enjoyed reading this post :)

Top comments (2)

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Bernd Wechner • • Edited

Not a bad summary. But falls short decisively with lines like: returns the given number of bytes (by default -1) from a specified file.

And yes? What does reading -1 bytes mean? And moreover it's more commonly a number of characters not bytes (we are well and truly into the Unicode era, and Python 3 like it or not). So it's bytes when the file is opened in byte mode else it's characters (which can be one or more bytes), and -1 is just the simplest case of a negative number, any negative number asking read() to read the rest of the file. Which is sort of worth saying in a beginners guide (far from obvious).

The introduction to readable() and writable() is good though. very pleased to see it as these are buried a bit deeply in IOBase documentation and overlooked in the formal Python tutorial: docs.python.org/3/tutorial/inputou...

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Aya Bouchiha •

I appreciate a lot your feedback, I will try more writing good summaries.
Thank you very much 😊