How to use python iter method to read a file

What is iter()?

iter()is a built-in function in Python that returns an iterator. An iterator is an object that allows you to access its elements one by one without loading all elements into memory at once. When we apply iter() to a file object,It allows us to read the file content line by line。
The basic syntax of iter():

iter(object[, sentinel])

• object: The object that needs to be converted into an iterator can be an iterable object (such as a list, string) or a custom object.
• sentinel (optional): used to generate an iterator with a function and stop iteration until the function returns the sentinel value.

Use iter() to read the file line by line

# Read file content line by linewith open('', 'r') as file:
    for line in iter(file):
        print(())  # Output each line of content

Use iter() and custom end tags

iter() can also be used in conjunction with a custom end tag (sentinel). When dealing with some custom read logic, iter() can end the iteration based on the conditions we provide. This method is often used to read fixed block or segmented data from a file until a specific tag is encountered.
Example: Use iter() and custom tags

def read_chunk(file_obj, chunk_size):
    return file_obj.read(chunk_size)
with open('', 'r') as file:
    for chunk in iter(lambda: read_chunk(file, 10), ''):  # 10 characters are read each time        print(chunk)

Iter() comparison with other methods of reading file

iter() is not the only way to read a file. Let's compare its advantages and disadvantages with other common file reading methods.

read() method
() Read the entire file at once, suitable for small files.

with open('', 'r') as file:
    content = ()
    print(content)

• Advantages: The code is simple and you can get all the contents of the file at once.
• Disadvantages: If the file is too large, it can cause memory overflow, especially files of several GB or larger.

readline() method

() Read one line of the file each time until the end of the file is encountered.

with open('', 'r') as file:
    while True:
        line = ()
        if not line:
            break
        print(())

• Advantages: Read line by line, suitable for large files, saving memory.
• Disadvantages: Compared with iter(), the code is slightly verbose and the file end condition must be processed manually.

readlines() method

() Read all rows at once and return a list containing the contents of each row.

with open('', 'r') as file:
    lines = ()
    for line in lines:
        print(())

• Advantages: You can directly obtain a list of all lines of the file, which is suitable for small files.
• Disadvantages: Similar to read(), for large files, it loads everything into memory, which consumes a lot of memory.

iter() method

with open('', 'r') as file:
    for line in iter(file):
        print(())

• Advantages: Simple and efficient, line-by-line reading, and low memory usage. It can be combined with for loops, making the code more concise and does not require explicit processing of file end conditions.
• Disadvantages: Compared with read(), in some scenarios, additional data processing may be required, such as processing the case of multiple rows being read simultaneously.

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