While loop read file python

While loop read file python. Nov 1, 2012 · I am reading serial data and writing to a csv file using a while loop. As with an if statement, a while loop can be specified on one line. The problem is that it doesn't work at all when reading textfiles. reason for not using while loop for this purpose would be helpful. If it is False, then the loop is terminated and control is passed to the next Aug 20, 2021 · This tutorial went over how while loops work in Python and how to construct them. listdir(directory): filename = os. For example, If you want to read the first five lines from a text file, run a loop five times, and use the readline() method in the loop’s body. pip install xlrd From there you can read the excel spreadsheet with the following. This only works with simple statements though. split(',')[7] GPSstr = tempstr. Print each city & the highest monthly average temperature. Step 3: Read the binary data. 12. import os directory = os. read([size]) Read at most size bytes from the file (less if the read hits EOF before obtaining size bytes). Python While Loop. You can analyze and transform the data using the available pandas tools. log(count); count++; } Feb 9, 2018 · I'm not sure if I'm missing something I'm still new at Python, but I am reading a lot of Matlab files in a folder. py"): # print(os. The following loop reads a file in chunks; it will call read at most once too many. sleep(1) # read file. Here you go Lim, that guy knows what he's doing, here is his best Idea: General approach #2: Read the entire file, store Sep 7, 2021 · I'm trying to figure out how to start a loop in Python that goes through a csv file. The module os is useful to work with directories. g. I'd like to understand the difference in RAM-usage of this methods when reading a large file in python. A while loop is a code construct that runs a set of statements, known as the loop body, while a given condition, known as the loop expression, is true. most_comments Mar 28, 2024 · A directory is capable of storing multiple files and python can support a mechanism to loop over them. Mar 7, 2019 · I'm trying to create a code that will use a function to check if the file exists and if not then it will ask the user for a file name again. Mar 19, 2017 · I have a while loop which asks for user input to produce a new population. A while loop is a part of a control flow Feb 13, 2017 · Whenever I do this, the while loop executes, goes through the file once, and then goes through the while loop till it stops, only going through the file once. Use strip to also remove whitespace at beginning. Jul 22, 2014 · Then measure the size of the tempfile, to get character-to-bytes ratio. Feb 13, 2015 · A simple implementation could be: time. Step 2) The open () function will return a file handler. Is there any possible way to do this? EDIT: Sorry for not clarifying the details. To read from a file, you first need to open the file and get a file object. @katrielalex - you're right, I fixed it. I don't have much experience in reading and writing to a file. This chapter will discuss some of the possibilities. If I understand correctly, you're trying to read the first 4 lines of your file. read_excel('your_excel. Following are the steps to read file line by line using readline() function. Jan 20, 2014 · input_str = sys. Before diving into the specifics of read() and readline(), let’s briefly overview the general process for reading data from files in Python: 1. – malfunctioning Dec 19, 2022 · Python makes it easy to work with files, and in this article, we’ll go over how to read and write files with Python. walk (), and glob module are the methods available to iterate over files. The below will parse the entire data area of your file, and do it in a way that is not arbitrary. I have to open a file in a while loop and do some stuff with the values of the file. 2 days ago · Input and Output — Python 3. A while loop is more commonly used to read a binary file fixed chunk by fixed chunk in Python. In Python an empty string is treated as False, therefore the while loop terminates. append (df) Complete Example. If you want, for example, to check a specific line for a length greater than 10, work with what you already have available. first_col = line[0] # If the column value is in the dict, increment its value. Jul 1, 2012 · Although the question asks specifically about the '\n' character, there is a more general issue of reading a line without the line-ending, whatever it may be for the file. Dec 28, 2013 · The first call to the read method actually returns all the content of the file. try: lists. Instead, enclose place the script into a loop for it to keep trying. >>> n = 5 >>> while n > 0: n -= 1; print(n) 4 3 2 1 0. If you try to use an iterator for a file where the pointer is at EOF it will just raise StopIteration and exit: that is why it counts zero in the second loop. name) for file_line in mf: When I come back around and loop for the second time, that first print statement should print the 5th line in the file. Sep 4, 2017 · Install xlrd (needed for working with Excel files). When the condition becomes false, execution comes out of the loop immediately, and the first statement after the while loop is executed. listdir (), os. It is a collection of files and subdirectories. endswith(". In this example, the condition for while will be True as long as the counter variable (count) is less Apr 20, 2012 · A fairly direct translation of your while loop that will work might be. Nov 3, 2011 · Python: For loop with files, how to grab the next line within forloop? 0 Is it possible to read a file line-by-line in while also skipping a given number of lines Python May 24, 2020 · This exercise assumes you have completed Programming Exercise 7, Random Number File Writer. rstrip() <continue processing row>. writer(f, dialect = 'excel') for line in g: tempstr = line. Input and Output ¶. Jan 1, 2015 · The "z = randrange (1,1000)" gives you one random number and the rest of your script reads the entire file and tries to match that number against the file. Mar 8, 2013 · According to Python documentation, you should use raw_input(): Consider using the raw_input () function for general input from users. average the number of comments across all posts. BTW, dont' use input as a variable name. scandir (), pathlib module, os. With a while-loop, however, this is not the case Oct 4, 2017 · Python read file in while loop. for row in file: row = row. for commonWord in commonWordList: commonWord = commonWord. Jan 4, 2023 · Reading a File Line-by-Line in Python with readline () Let's start off with the readline() method, which reads a single line, which will require us to use a counter and increment it: filepath = 'Iliad. 1 seconds (see my article Reading and Writing Files with Python). strip() But the more modern Python idiom for reading a file line-by-line is to use a for loop as Padraic Cunningham's answer uses. Method 1: Using listdir() In this method, we will use the os. tell () to get a pointer to where you are currently in the file (in terms of number of characters). Step 2: Create a binary file. I consider this a decent (if quick and dirty) answer: May 8, 2015 · I have a csv file that I'm trying to iterate through and have it do something only when a timestamp in it falls within a specified range. load(infile)) except (EOFError, UnpicklingError): break. Reading binary file in Python and looping over each byte. For that, a return value of 0 is used. Aug 29, 2019 · I tested and ran for loop on an open file to see if everything is working and it did. Or: Use notepad++ search and replace. Python solution for reading a text file into an if statement. randrange. tell() to get a pointer to where you are currently in the file(in terms of number of characters). We will first make some dummy data and then save that to some . keys(): This may run slower than the iterator-based for loop version, because iterators run at C language speed inside Python. The EOF marker in python is an empty string so what you have is pretty close to the best you are going to get without writing a function to wrap this up in an iterator. Python automatically checks for the End of file and closes the file for you (using the with open syntax). Some of these . May 27, 2021 · We can use many of these Python functions to read a file line by line. May 31, 2022 · Python has a well-defined methodology for opening, reading, and writing files. The . Mar 27, 2015 · while True: line=f. Then, multiply it with the ratio calculated earlier, to get the currentBytesRead value. let count = 0; while (count < 5) { console. line = file. When the condition in the while loop becomes false, the else block is executed. Also, the Python idiom for infinite loops is while 1, though that's nitpicky =). May 29, 2019 · Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. Aug 3, 2022 · Reading Large Text Files in Python. asm") or filename. txt files. We will write the dumy data to these files. os. Then measure the size of the tempfile, to get character-to-bytes ratio. Explain the loop construct in Python. Please can someone help? The for loop will iterate over each line in the file. You cannot "insert" into a text file. txt' with open (filepath) as fp: line = fp. edit apparently OP needs to read this file backwards: aaand after like an hour of research I failed multiple times to do it within memory constraints. Use str. What most answer here do is not wrong, but bad style. You should ask for a reason to use a while loop for this purpose. unpack("<I", len_name)[0] Jul 3, 2021 · file read methods readline(): Read a File Line by Line. >>> isinstance(sys. There are several ways to present the output of a program; data can be printed in a human-readable form, or written to a file for future use. You can read the lines of a file in Python using a for loop. For more refer to this article. Nov 17, 2023 · In use here is a while loop that continuously reads from the file as long as the readline() method keeps returning data. I want it to write the population to a text file every time the loop runs and replace what is already in there. by default, this method reads the first line in the file. In this article, we will see different methods to iterate over certain files in a given directory or subdirectory. fsencode(directory_in_str) for file in os. Read file in text mode. read() According to the documentation: file. To create a binary file in Python, You need to open the file in binary write mode ( wb ). readline() function. Feb 4, 2016 · I want the loop to break if any of the words from the input are not found in the text file, so far I have: Aug 10, 2021 · Python provides five different methods to iterate over files in a directory. Every time I write a while loop where the variable that the condition checks is set inside the loop (so that you have to initialize that variable before the loop, like in your second example), it doesn't feel right. Convert the city_temp to a list using . 0. While loop. Path containing different files: This will be used for all methods. The file has non ascii characters, such as Ö, for example. Whether it’s writing to a simple text file, reading a complicated server log, or even analyzing raw byte data, all of these situations require reading or writing a file. xlsx') df is now a DataFrame object. I want the user to be able to kill the while loop once they feel they have collected enough data. Sep 24, 2019 · Read in files using a for loop: dfs = list () for filename in filesnames: df = pd. Python Directory and Files Management; Python CSV: Read and Write CSV files; Mar 24, 2013 · Note that as of Python 3 the . We will therefore be using for loops to read in a . mf = open ( "myfile. while i < 6: print(i) i += 1. The script can be stopped with the KeyboardInterruption exception if the file is never created. Instead of printing the first 5 lines of text it will read through all and print them. split(',') # Get the value for the first column: first_col. Hence you should read it completely and then work with the single lines. Version 1, found here on stackoverflow: while True: data = file_object. Use if row[-1] == '\n': row = row[:-1] to only remove a newline. split(' ', 1) pronunciation[l]=r. Python can look and know that for a given . readline(). In this article, we will see how we can iterate over files in a directory in Python. In case the end of file (EOF) is reached the while loop stops and the file object is closed, freeing up the resources for other programs to use: # Define the name of the file to read from . Using the file object as an iterator gives you a lot of flexibility; you can read . The following code runs faster. Here's how you could do it with readline Jan 17, 2014 · I am currently in some truble regarding python and reading files. join(directory, filename)) continue else: continue Jul 31, 2019 · while loops: used when the size of data can't be known up front; In the case of a . Make Jan 3, 2019 · # [ ] The Weather: open file, read/print first line, convert line to list (splitting on comma) use a while loop to read the remaining lines from the file Assign remaining lines to a city_temp variable. Our first approach to reading a file in Python will be the path of least resistance: the readlines () method. read_csv (filename) dfs. But in this second run I get no values out of this file Jun 16, 2016 · Whenever you use a variable as a condition to an if or a while loop it is evaluated as a boolean value. Some applications for file manipulation in Python include: reading data for algorithm training and testing, reading files to create generative art, reporting, and reading configuration files. l, r=line. Open your file for reading (r) Read the whole file and save each line into a list (text) Loop through the list printing each line. for j in range(0, 1000): # Split the current line into a list: line. path. csv text/plain; charset=us-ascii This is a third-party file, and I get a new one every day, so I would rather not change it. While loops continue to loop through a block of code provided that the condition set in the while statement is True. close both, delete old, rename new to old name. Try it Yourself ». SystemRandom(). would read lines 20 through to 52; Python uses 0-based indexing, so line 1 is numbered 0. stdin. After iterating over the file, the pointer will be positioned at EOF (end of file) and the iterator will raise StopIteration which exits the loop. Steps to use file. Nov 21, 2020 · Reading two columns of numbers from a text file in python Hot Network Questions Is it correct to put a section separator (double thin lines) in the middle of a measure? Jul 16, 2019 · You can use itertools. csv file we are using in these notes can be found here. Apr 30, 2012 · Python 3. The iterator will return each line one by one, which can be processed. If there are multiple statements in the block that makes up the loop body, they can be separated by semicolons (; ): Python. islice() on the file object and use iteration to read only specific lines: for line in itertools. If the size argument is negative or omitted, read all data until EOF is reached. csv files will begin with "B00234" and some other would not. stdin, file) True. i am trying use while loop to run until a dict key value is set to True (or Ok . readline() in the loop. } Explanation of the Syntax: In C and C++, the while loop executes a block of code repeatedly as long as the specified condition evaluates to true. readline() cnt = 1 while line: Explain the loop construct in Python. readlines() for line in text: print line. Aug 10, 2021 · Python provides five different methods to iterate over files in a directory. Another alternative is to call read() to get all of the file's text in a single long string which you can then iterate over. while True: Jan 30, 2019 · 1. I just wanted to make sure I wasn't doing something inherently wrong or using poor style. New in Python 3. Oct 23, 2023 · We'll describe multiple ways in Python to read a file line by line with examples such as using readlines(), context manager, while loops. Use the file handler that open () returned inside a while loop to read lines. Using the readline() method, we can read a file line by line. Run. In this tutorial, you’ll learn: What makes up a file and why that’s important in Python. fsdecode(file) if filename. Dec 27, 2023 · The main difference between Python For Loop Versus Python While Loop is that Python for loop is usually used when the number of iterations is known, whereas Python while loop is used when the number of iterations is unknown. Python firstly checks the condition. elif commonWord == word: return True. csv file, there is a predictable amount of data. However, does not reads more than one line, even if n exceeds the length of the line. read example is not correct: read returns None when a non-blocking buffer has no data to offer at the moment, and doesn't indicate having reached EOF. islice(text_file, 19, 52): # do something with line. Whether next() is the real method to obtain the next line when using a file, I don't know. Then, while reading the large file, you can use filehandle. Mar 13, 2015 · The call to readline() on a line with no text will return "\n", while at the end of the file it will return "" (an empty string). text = f. append(pickle. How do I get my code to run through the file multiple times? The reason for this is because in my actual code I edit he text file in each loop. This loop should continue until an existing file name is Sep 7, 2023 · In this tutorial, you'll learn how you can work with files in Python by using built-in modules to perform practical tasks that involve groups of files, like renaming them, moving them around, archiving them, and getting their metadata. Example Get your own Python Server. Javascript. split('*')[0] print GPSstr. When a for-loop is used, the loop ends when the file's end is reached. I'm using a while loop to do this where I'm adding 30 seconds each time through, but for some reason it only iterates through the csv the first time it does the loop and not each addition time (although I Python while Loop; Python break and continue; Python pass Statement; Python Data types. Jan 17, 2023 · A file is a line iterator. Print i as long as i is less than 6: i = 1. Write another program that reads the random numbers from the file, display the numbers, and then display the following data: • The total of the numbers • The number of random numbers read from the file. wr = csv. I could be written in a little more pythonic way by changing the while like: while len_name: len_name = struct. Writing the file: Jul 7, 2014 · I have to read a text file into Python. So that my python while loop keep doing the loop by checking that dict key value. It starts with the keyword while, followed by a condition enclosed in parentheses. Open a File Object. 2. Typically, the while loop is used when it is impossible to determine the exact number of loop iterations in advance. txt", "r+" ) print ( "File to read: ", mf. 1. Nov 3, 2011 · Python: For loop with files, how to grab the next line within forloop? 0 Is it possible to read a file line-by-line in while also skipping a given number of lines Python Nov 18, 2018 · Tour Start here for a quick overview of the site Help Center Detailed answers to any questions you might have Jan 17, 2010 · Reading files is incredible fast. average score across all posts. In that case, the following read call will return the empty string (not None). Read a File Line by Line with the readlines () Method. One-Line while Loops. A directory is also known as a folder. You should never use except:; always specify the exception you are trying to catch (e. Use a while loop to implement repeating tasks. The file encoding is: file -bi test. This is not really what you need here, as highlighted by your comment. However, if there is a break statement inside the while loop block, the code exits the loop without executing the else block. import pandas as pd df = pd. Jan 25, 2011 · counts_dict = {} # Process only the first 1000 rows. The results are written into a new file. Feb 5, 2024 · Example 8: A while Loop with the else Clause. Reading a 100MB file takes less than 0. 6 version of the above answer, using os - assuming that you have the directory path as a str object in a variable called directory_in_str:. whatever). Example 1: Read Text File Line by Line – readline() In this example, we will use readline() function on the file stream to get next line in a loop. Jul 23, 2023 · Overview of Reading Files in Python. largest variable for the highest score and print title smallest variable for lowest score. This new file is then read in the next run of the while loop. import random. In each matlab file, there are multiple arrays and I can do things with each array like plot and find the average, max min etc. It returns a stream to the file. read(chunk_size) if not data: break. Asking for help, clarification, or responding to other answers. The syntax of the while loop in the simplest case looks like this: while some condition: a block of statements. csv file. Full documentation for read_excel(). Feb 14, 2024 · Syntax: while (condition) {. We can use the file object as an iterator. This is done with Python’s built-in open() function: file = open Jul 22, 2014 · In my earlier comment I meant, write a small amount of data(say a single line) to a tempfile, with the required encoding. Dec 27, 2014 · 1. yield data. split(',') for each . May 17, 2024 · While loop in JavaScript: JavaScript’s while loop syntax is similar to Python’s. Mar 24, 2013 · Note that as of Python 3 the . This method will open a file and split its contents into separate lines. rofile is a file object that I'm iterating through. Feb 22, 2024 · File iteration is a crucial process of working with files in Python. In simple words, The while loop enables the Python program to repeat a set of operations while a particular condition is true. . The while loop requires relevant variables to be ready, in this example we need to define an indexing variable, i, which we set to 1. Inside the while loop, we read the file one character at a time using the read() method. >>> import sys. Feb 8, 2013 · This loop will print all elements in the list. Use the following code for it: # Python 3 Code # Python Program to read file line by line # Using while statement # Open file. // Code block to be executed repeatedly as long as the condition is true. return False. I believe it would be a while loop (can't use pandas for this assignment) but I'm not sure how to start. Apr 16, 2020 · Using "for" Loop. It printed me a single list of all the words inside the txt file. The while-loop uses the Python readline () method to read the lines. Oct 6, 2010 · 10. Mar 20, 2020 · Basic idea of my script is to run python script continuously, till a file parameter is set to True (using different python script, or by manually changing it in different terminal). 2 Likes. if first_col in counts_dict. Thanks! – Aug 17, 2022 · Open the file in read mode using the open () function first to accomplish that. The loop continues executing as long as the condition evaluates to true. That's because input() is not what you expect: input ( [prompt]) Equivalent to eval(raw_input(prompt)). 5 is the pathlib module, which has a convenience method specifically to read in a file as bytes, allowing us to iterate over the bytes. process_data(piece) Version 2, I used this before I found the code above: Apr 29, 2015 · In that case just put the whole thing in a while loop guarded by a bool variable, and when you find an instance of the book title in the loop set the variable so that you exit the loop. The loop first evaluates the condition specified within the parentheses (). rstrip("\n") if commonWord <= word: break. And then I search for python repeat until to remind myself that I should just accept that feeling :) – Jun 25, 2021 · print(count) count = count + 1. Provide details and share your research! But avoid …. I Aug 25, 2023 · To read a binary file in Python, first, we need to open it in binary mode (‘”rb”‘). This will not read the whole file into memory and it’s suitable to read large files in Python. The regular expression is a 1:1 representation of a line of data. csv, there is a specific number of rows. Create an Infinite Sep 7, 2021 · need a variable to control the loop reading the lines while loop. One of the most common tasks that you can do with Python is reading and writing files. The process of accessing and processing each item in any collection is called File iteration in Python, which involves looping through a folder and perform operation on each file. 3 documentation. Note: remember to increment i, or else the loop will continue forever. except PicklingError: ). Done. Use a regular expression with named groups. python iterate though text file until condition is met. I am reading in a file and wonder if there's a way to read the next line in a for loop? May 2, 2017 · It feels strange to be looping over a file object and then having a nested loop looping over that same file object as if it would somehow reset the line counter, but it obviously works as Python seems to keep track regardless of how many nested loops I use. raise ValueError("%s isn't a file!" % file_path) You wait a certain amount of time after each check, and then read the file when the path exists. Open a new file, read the other file, copy every line over into the new file, if you find your special line, write the two other lines into the new file -do until old file read completely. Here is the code snippet to read large file in Python by treating it as an iterator. My code works perfectly and reads the data correctly. In Python, a while loop can be used with an else clause. Use the file handler inside your for-loop and read all the lines from the given file line-by-line. It takes a parameter n, which specifies the maximum number of bytes that will be read. readline() if not line: break. rstrip to remove any whitespace, including newlines, at the end of a string. At each iteration, once the loop statement is executed, the loop expression is evaluated again. randrange = random. The while loop version runs Python byte code through the Python virtual machine. my expectation is to check if the word is in the words_list and continue, but now what happens is, it will always print (word is not in the list), even if I type the word that is indeed in the list. We can use the ‘open ()’ function to achieve this. We then check if we’ve reached the end of the file (if not c), and if so, we break out of the loop. I want to be able to read one set until the next <string> is reached (and use its data), then read trough the next set of data until the next <string> is reached, and so on until the end of the file. Apr 13, 2012 · When reading a file in chunks rather than with read(), you know you've hit EOF when read returns less than the number of bytes you requested. Compare this: Mar 9, 2024 · Step 1) First, open the file using Python open () function in read mode. csv and . 7. The for loop automatically terminates when the end of the file is reached. You should either do this by iterating through the file and breaking after 4 lines have been read or simply using readline instead of read. lis This will store the previous line in prevLine while you are looping. Jul 2, 2013 · per file. 3. Using this approach, we Mar 27, 2023 · Method 2: Read a File Line by Line using readline () readline () function reads a line of the file and return it in the form of the string. The argument 1 tells Python to read only one character at a time from the file. Step 3) Once done, close the file handler using the close () function. dh bc bj hd qg bl oj vo oi eo