File handling is an important aspect of programming, especially when dealing with large amounts of data. Python provides a convenient way to work with files through its built-in “open” function. This function opens a file, allowing you to perform various operations such as reading, writing, or appending to the file. The file can be in various formats such as text, binary, or even pickled. When you open a file, it must be closed after use to ensure that the data stored in the file is properly saved.
Reading from a file is achieved by using the “read” method, which can be used to read the entire contents of a file, or a specified number of characters. If you want to read the file line by line, you can use the “readline” or “readlines” methods. Writing to a file is done using the “write” method, which takes a string as input and writes it to the file. If you want to append data to an existing file, you can open the file in “append” mode.
Pickling is a process that serializes Python objects, allowing you to store the object in a file and retrieve it later. This is done using the “pickle” module, which provides functions to pickle and unpickle Python objects. This process of pickling and unpickling is also known as serialization and deserialization, respectively.
Differentiate between:
- text file and binary file
- readline() and readlines()
- write() and writelines()
Differentiate between text file and binary file
A text file is a type of file that contains plain text and can be edited using a text editor. It has a human-readable format and uses ASCII or Unicode encoding to represent characters.
A binary file, on the other hand, is a type of file that contains data in binary format, which is not human-readable. It is used to store executable files, images, audio, and other non-text data. The data in a binary file is stored in a series of 1s and 0s, and can only be read and processed by a computer program.
Differentiate between readline() and readlines()
In Python, readline() and readlines() are both methods for reading files, but they behave differently:
readline() reads a single line from a file and returns it as a string. Here’s an example of how to use readline():
1 2 3 4 5 | with open("file.txt") as file: line = file.readline() while line: print(line.strip()) line = file.readline() |
readlines() reads the entire file and returns it as a list of strings, where each string is a line from the file. Here’s an example of how to use readlines():
1 2 3 4 | with open("file.txt") as file: lines = file.readlines() for line in lines: print(line.strip()) |
Note that readlines() reads the entire file into memory, so it may not be suitable for very large files. On the other hand, readline() reads one line at a time, which can be more memory-efficient for large files.
Write the use and syntax for the following methods:
- open()
- read()
- seek()
- dump()
The use and syntax for the open()
In Python, the open() function is used to open a file for reading or writing. The syntax for open() is as follows:
1 | open(file, mode='r', buffering=-1, encoding=None, errors=None, newline=None, closefd=True, opener=None) |
Here’s a brief explanation of the parameters:
file: A string or an integer file descriptor that specifies the file to be opened.mode: A string that specifies the mode in which the file should be opened. The default value is'r'which means “read”. Other possible values are'w'(write),'a'(append),'x'(exclusive creation), and'b'(binary).buffering: An integer that specifies the buffering policy for the file. A value of 0 means no buffering, 1 means line buffering, and larger values specify the buffer size. The default value is -1, which means the system default buffering is used.encoding: A string that specifies the encoding to use for text files. This parameter is not used for binary files.errors: A string that specifies how to handle encoding errors. The default value is'strict'.newline: A string that specifies how to handle newlines in text files. The default value isNone, which means the newline handling is platform dependent.closefd: A Boolean that specifies whether the file descriptor should be closed when the file object is closed. The default value isTrue.opener: A function that is called to open the file. The default value isNone.
Here’s an example of how to use open() to read a text file:
1 2 3 | with open("file.txt") as file: contents = file.read() print(contents) |
And here’s an example of how to use open() to write to a text file:
1 2 | with open("file.txt", "w") as file: file.write("Hello, world!") |
The use and syntax for the read()
In Python, the read() method is used to read the contents of a file. The syntax for read() is as follows:
1 | file.read([size]) |
Here’s a brief explanation of the parameters:
size(optional): An integer that specifies the maximum number of bytes to be read. Ifsizeis not specified, the method will read the entire contents of the file.
It’s important to note that the read() method can be used only after opening a file using the open() function. Here’s an example of how to use read() to read the contents of a text file:
1 2 3 | with open("file.txt") as file: contents = file.read() print(contents) |
In the example above, the with statement is used to open the file, and the read() method is used to read the entire contents of the file. The contents are stored in the contents variable, and then printed to the console.
The use and syntax for the seek()
In Python, the seek() method is used to change the file position of a file. The syntax for seek() is as follows:
1 | file.seek(offset, whence=0) |
Here’s a brief explanation of the parameters:
offset: An integer that specifies the number of bytes to move the file position.whence(optional): An integer that specifies the reference point foroffset. The default value is 0, which means the beginning of the file. Other possible values are 1 (current position), and 2 (end of file).
It’s important to note that the seek() method can be used only after opening a file using the open() function. Here’s an example of how to use seek() to change the file position:
1 2 3 4 5 6 | with open("file.txt") as file: print(file.tell()) # prints the current file position file.seek(5) # moves the file position 5 bytes from the beginning of the file print(file.tell()) # prints the new file position contents = file.read() print(contents) |
In the example above, the with statement is used to open the file, and the seek() method is used to change the file position. The tell() method is used to retrieve the current file position. The contents are then read and printed to the console.
The use and syntax for the dump()
The dump() function is part of the pickle module in Python, which is used for serializing and deserializing Python objects to and from binary files. The syntax for dump() is as follows:
1 | pickle.dump(obj, file, protocol=None, *, fix_imports=True) |
Here’s a brief explanation of the parameters:
obj: The Python object to be serialized and written to the file.file: A file-like object, or a string representing the file name, where the serialized object will be written.protocol(optional): An integer that specifies the protocol version to be used. The default value isNone, which means the highest protocol version will be used.fix_imports(optional): A Boolean that specifies whether to try to map the new Python 3 names to the old module names used in Python 2. The default value isTrue.
Here’s an example of how to use dump() to write a Python object to a binary file:
1 2 3 4 5 6 7 8 | import pickle data = {'a': [1, 2.0, 3, 4+6j], 'b': ('string', u'Unicode string'), 'c': None} with open('data.pickle', 'wb') as file: pickle.dump(data, file) |
In the example above, the pickle module is imported, and a dictionary object is created. The dump() function is then used to write the object to a binary file named data.pickle. The 'wb' mode is used to open the file in binary write mode.
Write the file mode that will be used for opening the following files. Also, write the Python statements to open the following files:
- a text file “example.txt” in both read and write mode
- a binary file “bfile.dat” in write mode
- a text file “try.txt” in append and read mode
- a binary file “btry.dat” in read only mode
Here are the file modes and the corresponding Python statements to open the files:
a) A text file “example.txt” in both read and write mode: File mode: 'r+' Python statement:
1 2 | with open("example.txt", 'r+') as file: # code to read and write the file |
b) A binary file “bfile.dat” in write mode: File mode: 'wb' Python statement:
1 2 | with open("bfile.dat", 'wb') as file: # code to write the binary file |
c) A text file “try.txt” in append and read mode: File mode: 'a+' Python statement:
1 2 | with open("try.txt", 'a+') as file: # code to read and write (append) to the file |
d) A binary file “btry.dat” in read-only mode: File mode: 'rb' Python statement:
1 2 | with open("btry.dat", 'rb') as file: # code to read the binary file |
Note: In all the above statements, the with statement is used to open the file, which automatically closes the file after the indented block of code has been executed.
Why is it advised to close a file after we are done with the read and write operations? What will happen if we do not close it? Will some error message be flashed?
It is advised to close a file after you are done with the read and write operations for several reasons:
- Resource Management: When a file is opened, the operating system allocates system resources, such as memory and handles, to manage the file. If the file is not closed properly, these resources are not freed and remain occupied, which can lead to a shortage of resources over time and cause performance issues. Closing the file releases these resources and ensures they can be used by other processes.
- Data Loss: If a file is opened but not closed, it is possible that changes made to the file may not be saved. In the case of a system crash or power failure, the data can be lost. Closing the file ensures that the data is saved and any changes are committed to the file.
- Consistency: If multiple processes or threads are accessing the same file, leaving a file open can lead to inconsistent data, as one process may be making changes to the file while another is trying to read it. Closing the file ensures that the data is consistent and that the file is not in use by any other process.
No, not necessarily. The lack of closing a file does not result in an error message in most cases. However, the consequences of not closing a file can lead to other problems, such as data loss or resource shortages, which can cause errors in other parts of the program.
In Python, it is a good practice to use the with statement when working with files. The with statement ensures that the file is closed automatically when the block of code is executed, even if an exception is raised. This helps to prevent leaving files open and ensures proper resource management.
What is the difference between the following set of statements (a) and (b):
1 2 3 | # (a) P = open(“practice.txt”,”r”) P.read(10) |
1 2 3 | # (b) with open(“practice.txt”, “r”) as P: x = P.read() |
The difference between the two sets of statements is as follows:
1 2 3 | # (a) P = open(“practice.txt”,”r”) P.read(10) |
In this set of statements, the file “practice.txt” is opened using the open() function and assigned to the variable P. The read(10) method is then used to read the first 10 characters of the file. However, the file is not closed after the read operation.
1 2 3 | # (b) with open(“practice.txt”, “r”) as P: x = P.read() |
In this set of statements, the file “practice.txt” is opened using the with statement and the open() function. The file is assigned to the variable P and the read() method is used to read the entire contents of the file into the variable x. The with statement automatically closes the file after the block of code is executed, so there is no need to close the file explicitly.
In conclusion, it is always recommended to use the with statement when working with files in Python, as it ensures that the file is closed automatically and helps to prevent resource leaks and data loss.
Write a command(s) to write the following lines to the text file named hello.txt. Assume that the file is opened in append mode. “ Welcome my class” “It is a fun place” “You will learn and play”
The following code writes the lines “Welcome my class”, “It is a fun place”, and “You will learn and play” to a text file named “hello.txt” in append mode:
1 2 3 4 | with open("hello.txt", "a") as file: file.write("Welcome my class\n") file.write("It is a fun place\n") file.write("You will learn and play\n") |
Here, the with statement is used to open the file “hello.txt” in append mode ("a"). The lines are written to the file using the write() method, and each line is separated by a newline character (\n). The with statement ensures that the file is automatically closed after the block of code is executed.
Write a Python program to open the file hello.txt used in question no 6 in read mode to display its contents. What will be the difference if the file was opened in write mode instead of append mode?
Here is the code to write the lines “Welcome my class”, “It is a fun place”, and “You will learn and play” to the text file named “hello.txt” in append mode:
1 2 3 4 | with open("hello.txt", "a") as file: file.write("Welcome my class\n") file.write("It is a fun place\n") file.write("You will learn and play\n") |
And here is the code to open the file “hello.txt” in read mode and display its contents:
1 2 3 | with open("hello.txt", "r") as file: contents = file.read() print(contents) |
In this code, the file “hello.txt” is opened using the with statement in read mode ("r"). The contents of the file are read into the variable contents using the read() method and then printed to the screen using the print() function.
If the file was opened in write mode ("w") instead of append mode ("a"), the contents of the file would be overwritten instead of appended. This means that any existing data in the file would be deleted and only the new data would be written to the file. If the file did not exist, a new file would be created.
Write a program to accept string/sentences from the user till the user enters “END” to. Save the data in a text file and then display only those sentences which begin with an uppercase alphabet.
Here is a Python program that accepts sentences from the user until the user enters “END” and then saves the data to a text file and displays only the sentences that begin with an uppercase alphabet:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | sentences = [] sentence = input("Enter a sentence (Enter 'END' to stop): ") while sentence != "END": sentences.append(sentence) sentence = input("Enter a sentence (Enter 'END' to stop): ") with open("sentences.txt", "w") as file: for sentence in sentences: file.write(sentence + "\n") with open("sentences.txt", "r") as file: contents = file.readlines() for sentence in contents: if sentence[0].isupper(): print(sentence) |
In this code, the user is prompted to enter a sentence using the input() function. The entered sentences are stored in a list called sentences until the user enters “END”. The list of sentences is then saved to a text file named “sentences.txt” in write mode ("w") using the with statement. The contents of the file are read into the variable contents using the readlines() method, which returns a list of strings, where each string represents a line in the file. Finally, the code iterates over the list of sentences and prints the sentences that begin with an uppercase alphabet by checking the first character of each sentence using the isupper() method.
Define pickling in Python. Explain serialization and deserialization of Python object.
Pickling in Python is a process of converting a Python object hierarchy into a byte stream that can be stored in a file or transmitted over a network. This byte stream can then be deserialized back into a Python object hierarchy. This process is known as serialization and deserialization.
Serialization in Python refers to the process of converting a Python object into a stream of bytes, which can be stored in a file or transmitted over a network. This stream of bytes can be reconstructed back into a Python object using deserialization. The pickle module in Python provides functions for serializing and deserializing Python objects.
Deserialization in Python refers to the process of converting a stream of bytes into a Python object. This stream of bytes is created by the serialization process and can be stored in a file or transmitted over a network. The pickle module in Python provides functions for deserializing a stream of bytes back into a Python object.
To summarize, pickling in Python provides a mechanism for serializing and deserializing Python objects into a byte stream that can be stored in a file or transmitted over a network. This process allows us to persist Python objects between different runs of a program or transfer data between different processes or systems.
Write a program to enter the following records in a binary file:
1 2 3 4 | Item_No integer Item_Name string Qty integer Price float |
Number of records to be entered should be accepted from the user. Read the file to display the records in the following format:
1 2 3 4 5 | Item No: Item Name : Quantity: Price per item: Amount: ( to be calculated as Price * Qty) |
Here is a program to implement the functionality described above:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 | import struct def write_binary_file(num_records): # Open the file in binary write mode with open("item_records.bin", "wb") as binary_file: # Loop over the number of records for i in range(num_records): # Accept the input values for each record item_no = int(input("Enter item number: ")) item_name = input("Enter item name: ").encode() qty = int(input("Enter quantity: ")) price = float(input("Enter price: ")) # Pack the values into binary format binary_file.write(struct.pack("i", item_no)) binary_file.write(struct.pack("{}s".format(len(item_name)), item_name)) binary_file.write(struct.pack("i", qty)) binary_file.write(struct.pack("f", price)) def read_binary_file(): # Open the file in binary read mode with open("item_records.bin", "rb") as binary_file: while True: # Read the values from the file and unpack them item_no = binary_file.read(4) if not item_no: # End of file break item_no = struct.unpack("i", item_no)[0] # Read the string value name_len = binary_file.read(4) name_len = struct.unpack("i", name_len)[0] item_name = binary_file.read(name_len).decode() qty = binary_file.read(4) qty = struct.unpack("i", qty)[0] price = binary_file.read(4) price = struct.unpack("f", price)[0] # Calculate the amount amount = price * qty # Display the values in the required format print("Item No:", item_no) print("Item Name:", item_name) print("Quantity:", qty) print("Price per item:", price) print("Amount:", amount) # Accept the number of records from the user num_records = int(input("Enter number of records: ")) # Write the records to the binary file write_binary_file(num_records) # Read the binary file and display the records read_binary_file() |
In this program, we use the struct module to pack and unpack the values in binary format. The write_binary_file function accepts the number of records as input and writes the records to the binary file item_records.bin in binary write mode. The read_binary_file function reads the binary file and displays the records in the required format. The amount is calculated as the product of the price and quantity.
