Open the text file with with open(...), then loop over the file object: for line in file. This processes lines one at a time without first loading the whole file into memory.
Read a text file one line at a time
For ordinary sequential processing, iterate directly over the file object. Specify the file’s known encoding; UTF-8 is a common choice when it matches the file.
with open("path/to/file.txt", encoding="utf-8") as file:
for line in file:
process(line)
Replace "path/to/file.txt" with the file’s path and process(line) with the work you want to do for each line, such as checking it or extracting a value. The Python tutorial describes looping over a file object as memory efficient, fast, and simple. Iteration avoids collecting every line into a list first.
Choose the right reading method
| Method | What it does | Use it when |
|---|---|---|
for line in file |
Yields lines successively. | You want to process a text file from beginning to end without collecting all its lines. |
file.readline() |
Returns one line per call; returns an empty string at end of file. | Your code needs to request each next line explicitly. |
file.readlines() or list(file) |
Collects the file’s lines in a list. | You need the lines together in memory. |
file.read() without a size |
Reads the entire file into one string. | You need the whole text at once and the file size is suitable for available memory. |
For large inputs, prefer iteration or repeated readline() when you only need sequential processing. readlines(), list(file), and an unbounded read() materialize the content in memory. The Python tutorial’s file-object methods documents these options.
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Handle newlines and blank lines
In text mode, Python normalizes platform-specific line endings. A line produced by iteration or readline() usually still ends with a newline character. If you print it unchanged, suppress print()’s additional newline:
with open("path/to/file.txt", encoding="utf-8") as file:
for line in file:
print(line, end="")
A final line does not have to end with a newline in the source file. Also distinguish a blank line from end of file: readline() returns a newline string for a blank line, while an empty string means there is no line left to read.
Use a context manager and an explicit encoding
The with statement closes the file when the block ends, including when an exception interrupts the block. It is a reliable default for file-reading code. Python’s default text encoding can vary by platform, so specify the encoding when it is known. Use encoding="utf-8" for a UTF-8 file; if the file uses another encoding, specify that encoding instead. See the official file I/O tutorial.
Read binary files as bytes
The examples above are for text. Text mode decodes file contents into strings and handles newlines. For binary formats such as images or executables, open the file in binary mode instead; binary reads return bytes and avoid text-mode newline conversion. Do not treat binary content as ordinary text.
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In this binary example, iteration yields chunks separated by newline bytes, not decoded text lines. For a format-specific binary parser, follow that format’s structure rather than assuming newline-separated records.
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