How to Read a File Until a Specific Character in Python
This guide describes how to read a file in Python up to a specific character. This is useful for parsing data where you only need a portion of the file or when you're looking for a specific delimiter. We'll cover using split()
, a while
loop with character-by-character reading.
The code examples assume that you have an example.txt file located in the same directory and that contains what follows:
tutorial
reference
.com
!
one
two
three
Reading Until a Character with split()
(for smaller files)
If your file is relatively small and fits comfortably in memory, the simplest way to read up to a specific character is to read the entire file and then use the split()
method:
with open('example.txt', 'r', encoding='utf-8') as file:
contents = file.read()
character = '!'
result = contents.split(character, 1)[0] # Split only once
print(result)
Output:
tutorial
reference
.com
- The
with open()
opens the file in read mode ('r'
) with UTF-8 encoding, and automatically closes the file when the block is finished. file.read()
reads the entire file content into a single string. This is fine for small files, but inefficient for very large files.- The
.split(character, 1)
method is used to split the file content at the specified character. maxsplit=1
limits the number of times the string is split.[0]
gets the part of the string before the first occurrence of the delimiter.
Reading Until a Character with a while
Loop (for large files)
For large files that might not fit in memory, it's more efficient to read the file character by character until you encounter the target character:
with open('example.txt', 'r', encoding='utf-8') as file:
result = ''
stop_char = '!'
while True:
char = file.read(1) # Read one character at a time
if char == stop_char:
break # Stop when the character is found
if not char: # Reached end of file
print('Reached end of file')
break
result += char
print(result)
Output (assuming example.txt contains "tutorial\nreference\n.com\n!\none\ntwo\nthree"):
tutorial
reference
.com
file.read(1)
reads one character at a time. This avoids loading the entire file into memory.- The
while True
loop continues indefinitely until explicitly broken. if char == stop_char:
checks if the current character is the target character. If so,break
exits the loop.if not char:
checks if we've reached the end of the file (an empty string is returned byread()
at EOF). If so, we print a message andbreak
.result += char
: Appends the current character to theresult
string.
This approach is memory-efficient because it processes the file one character at a time.