Python while end of file

[python] How to while loop until the end of a file in Python without checking for empty line?

I’m writing an assignment to count the number of vowels in a file, currently in my class we have only been using code like this to check for the end of a file:

vowel=0 f=open("filename.txt","r",encoding="utf-8" ) line=f.readline().strip() while line!="": for j in range (len(line)): if line[j].isvowel(): vowel+=1 line=f.readline().strip() 

But this time for our assignment the input file given by our professor is an entire essay, so there are several blank lines throughout the text to separate paragraphs and whatnot, meaning my current code would only count until the first blank line.

Is there any way to check if my file has reached its end other than checking for if the line is blank? Preferably in a similar fashion that I have my code in currently, where it checks for something every single iteration of the while loop

The answer is

Don’t loop through a file this way. Instead use a for loop.

for line in f: vowel += sum(ch.isvowel() for ch in line) 

In fact your whole program is just:

VOWELS = # I'm assuming this is what isvowel checks, unless you're doing something # fancy to check if 'y' is a vowel with open('filename.txt') as f: vowel = sum(ch in VOWELS for line in f for ch in line.strip()) 

That said, if you really want to keep using a while loop for some misguided reason:

while True: line = f.readline().strip() if line == '': # either end of file or just a blank line. # we'll assume EOF, because we don't have a choice with the while loop! break 

reads all file to a memory, and that can be a problem.

My offer is to change the original source by replacing stripping and checking for empty line. Because if it is not last line — You will receive at least newline character in it (‘\n’). And ‘.strip()’ removes it. But in last line of a file You will receive truely empty line, without any characters. So the following loop will not give You false EOF, and You do not waste a memory:

with open("blablabla.txt", "r") as fl_in: while True: line = fl_in.readline() if not line: break line = line.strip() # do what You want 

Find end position of file:

f = open("file.txt","r") f.seek(0,2) #Jumps to the end f.tell() #Give you the end location (characters from start) f.seek(0) #Jump to the beginning of the file again 

if line == '' and f.tell() == endLocation: break 

I discovered while following the above suggestions that for line in f: does not work for a pandas dataframe (not that anyone said it would) because the end of file in a dataframe is the last column, not the last row. for example if you have a data frame with 3 fields (columns) and 9 records (rows), the for loop will stop after the 3rd iteration, not after the 9th iteration. Teresa

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Python End of File

1. Use file.read() to Find End of File in Python
2. Use the readline() Method With a while Loop to Find End of File in Python
3. Use Walrus Operator to Find End of File in Python

EOF stands for End Of File . This is the point in the program where the user cannot read the data anymore. It means that the program reads the whole file till the end. Also, when the EOF or end of the file is reached, empty strings are returned as the output. So, a user needs to know whether a file is at its EOF.

This tutorial introduces different ways to find out whether a file is at its EOF in Python.

Use file.read() to Find End of File in Python

The file.read() method is a built-in Python function used to read the contents of a given file. If the file.read() method returns an empty string as an output, which means that the file has reached its EOF.

with open("randomfile.txt", "r") as f:  while True:  file_eof = file_open.read()  if file_eof == '':  print('End Of File')  break 

Note that when we call the open() function to open the file at the starting of the program, we use «r» as the mode to read the file only. Finally, we use the if conditional statement to check the returned output at the end is an empty string.

Use the readline() Method With a while Loop to Find End of File in Python

The file.readline() method is another built-in Python function to read one complete text file line.

The while loop in Python is a loop that iterates the given condition in a code block till the time the given condition is true. This loop is used when the number of iterations is not known beforehand.

Using the while loop with the readline() method helps read lines in the given text file repeatedly.

file_path = 'randomfile.txt'  file_text = open(file_path, "r")  a = True  while a:  file_line = file_text.readline()  if not file_line:  print("End Of File")  a = False  file_text.close() 

The while loop will stop iterating when there will be no text left in the text file for the readline() method to read.

Use Walrus Operator to Find End of File in Python

The Walrus operator is a new operator in Python 3.8. It is denoted by := . This operator is basically an assignment operator which is used to assign True values and then immediately print them.

file = open("randomfile.txt", "r")  while (f := file.read()):  process(f)  file.close() 

Here, the True values are the characters that the read() function will read from the text file. That means it will stop printing once the file is finished.

Lakshay Kapoor is a final year B.Tech Computer Science student at Amity University Noida. He is familiar with programming languages and their real-world applications (Python/R/C++). Deeply interested in the area of Data Sciences and Machine Learning.

Related Article — Python File

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How to Check if it is the End of File in Python

If the end of the file (EOF) is reached in Python the data returned from a read attempt will be an empty string.

Let’s try out two different ways of checking whether it is the end of the file in Python.

Calling the Read Method Again

We can call the Python .read() method again on the file and if the result is an empty string the read operation is at EOF.

Some content. Another line of content. 

open_file = open("file.txt", "r") text = open_file.read() eof = open_file.read() if eof == '': print('EOF') 

Read Each Line in a while Loop

Another option is to read each line of the file by calling the Python readline() function in a while loop. When an empty string is returned we will know it is the end of the file and we can perform some operation before ending the while loop.

Some content. Another line of content. 

path = 'file.txt' file = open(path, 'r') x = True while x: line = file.readline() if not line: print('EOF') x = False file.close() 

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Python while end of file

Last updated: Feb 22, 2023
Reading time · 4 min

# Table of Contents

# Read a file until a specific Character in Python

To read a file until a specific character:

1. Open the file in reading mode.
2. Use the file.read() method to read the file’s contents into a string.
3. Use the str.split() method to split the file on the given character.
4. Access the list at index 0 .

Copied! 
with open('example.txt', 'r', encoding='utf-8') as file: contents = file.read() character = '!' result = contents.split(character) print(result) # 👉️ ['bobby\nhadz\n.com\n', '\none\ntwo\nthree'] # bobby # hadz # .com print(result[0]) 

The code sample assumes that you have an example.txt file located in the same directory.

Copied! 
bobby hadz .com ! one two three 

We used the with statement to open the file in reading mode.

The statement automatically takes care of closing the file for us.

The file.read() method is used to read the contents of the entire file into a string.

If you work with very large files that you don’t want to load in memory, scroll down to the next subheading.

Once we have the file’s contents stored in a string, we use the str.split() method to split the string on the given character.

The str.split() method splits the string into a list of substrings using a delimiter.

The method takes the following 2 parameters:

Name	Description
separator	Split the string into substrings on each occurrence of the separator
maxsplit	At most maxsplit splits are done (optional)

# Only getting the part of the file before the character

If you only need the part of the file before the character, set the maxsplit() argument to 1 to only split the string once.

Copied! 
with open('example.txt', 'r', encoding='utf-8') as file: contents = file.read() character = '!' result = contents.split(character, 1) print(result) # 👉️ ['bobby\nhadz\n.com\n', '\none\ntwo\nthree'] # bobby # hadz # .com print(result[0]) 

This is a bit more performant if the character is contained multiple times in the file because the string is only split on the first occurrence of the given character.

Alternatively, you can use a while loop.

# Read a file until a specific Character using a while loop

This is a three-step process:

1. Open the file in reading mode.
2. Use the file.read(1) method to read the file character by character in a while loop.
3. Once the stop character is found, exit the loop.

Copied! 
with open('example.txt', 'r', encoding='utf-8') as file: result = '' stop_char = '!' while True: char = file.read(1) if char == stop_char: break if not char: print('Reached end of file') break result += char # bobby # hadz # .com print(result) 

The code sample assumes that you have an example.txt file located in the same directory.

Copied! 
bobby hadz .com ! one two three 

We used a while True loop to iterate until we reach the end of the file.

The file.read() method takes a size argument that represents the number of characters to read from the file.

If you are reading a file in binary mode, then size represents the size of bytes to be read from the file.

We set the size argument to 1 to read the file character by character.

If the end of the file has been reached, the file.read() method returns an empty string.

On each iteration, we check if the current character is equal to the stop character.

If the condition is met, we exit the loop, otherwise, we add the character to the result string.

The break statement breaks out of the innermost enclosing for or while loop.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

• Remove the Extension from a Filename in Python
• How to save user input to a File in Python
• Write a List of Tuples to a File in Python
• Write a String to a File on a New Line every time in Python
• How to check if a File is Empty in Python
• Count number of unique Words in a String or File in Python
• Create a file name using Variables in Python
• How to recursively delete a Directory in Python
• pygame.error: video system not initialized [Solved]
• OSError: [Errno 8] Exec format error in Python [Solved]
• How to open an HTML file in the Browser using Python
• Pandas: Changing the column type to Categorical

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