python read single line from file as string [closed]
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I have a text file with a bunch of numbers then another line of numbers and another and another etc. with n number of lines how can I read it and store the lines into n number of strings?
2 Answers 2
file.readline([size])
Read one entire line from the file. A trailing newline character is kept in the string (but may be absent when a file ends with an incomplete line). [6] If the size argument is present and non-negative, it is a maximum byte count (including the trailing newline) and an incomplete line may be returned. When size is not 0, an empty string is returned only when EOF is encountered immediately.
file.readlines([sizehint])
Read until EOF using readline() and return a list containing the lines thus read. If the optional sizehint argument is present, instead of reading up to EOF, whole lines totalling approximately sizehint bytes (possibly after rounding up to an internal buffer size) are read. Objects implementing a file-like interface may choose to ignore sizehint if it cannot be implemented, or cannot be implemented efficiently.
Good resources, but I think that if this guy is new (which I think he is) he may not completely understand what this documentation means by some of this. I know I didn’t understand what this stuff meant when I was starting out.
I think that if this guy is new (which I think he is) he may not completely understand what this documentation means by some of this. Isn’t documentation there so that one can refer to it when he/she can’t understand something??
Python Read Text File
Summary: in this tutorial, you learn various ways to read text files in Python.
TL;DR
The following shows how to read all texts from the readme.txt file into a string:
with open('readme.txt') as f: lines = f.readlines()Code language: Python (python)Steps for reading a text file in Python
To read a text file in Python, you follow these steps:
- First, open a text file for reading by using the open() function.
- Second, read text from the text file using the file read() , readline() , or readlines() method of the file object.
- Third, close the file using the file close() method.
1) open() function
The open() function has many parameters but you’ll be focusing on the first two:
open(path_to_file, mode)Code language: Python (python)The path_to_file parameter specifies the path to the text file.
If the program and file are in the same folder, you need to specify only the filename of the file. Otherwise, you need to include the path to the file as well as the filename.
To specify the path to the file, you use the forward-slash ( ‘/’ ) even if you’re working on Windows.
For example, if the file readme.txt is stored in the sample folder as the program, you need to specify the path to the file as c:/sample/readme.txt
The mode is an optional parameter. It’s a string that specifies the mode in which you want to open the file. The following table shows available modes for opening a text file:
| Mode | Description |
|---|---|
| ‘r’ | Open for text file for reading text |
| ‘w’ | Open a text file for writing text |
| ‘a’ | Open a text file for appending text |
For example, to open a file whose name is the-zen-of-python.txt stored in the same folder as the program, you use the following code:
f = open('the-zen-of-python.txt','r')Code language: Python (python) The open() function returns a file object which you will use to read text from a text file.
2) Reading text methods
The file object provides you with three methods for reading text from a text file:
- read(size) – read some contents of a file based on the optional size and return the contents as a string. If you omit the size, the read() method reads from where it left off till the end of the file. If the end of a file has been reached, the read() method returns an empty string.
- readline() – read a single line from a text file and return the line as a string. If the end of a file has been reached, the readline() returns an empty string.
- readlines() – read all the lines of the text file into a list of strings. This method is useful if you have a small file and you want to manipulate the whole text of that file.
3) close() method
The file that you open will remain open until you close it using the close() method.
It’s important to close the file that is no longer in use for the following reasons:
- First, when you open a file in your script, the file system usually locks it down so no other programs or scripts can use it until you close it.
- Second, your file system has a limited number of file descriptors that you can create before it runs out of them. Although this number might be high, it’s possible to open a lot of files and deplete your file system resources.
- Third, leaving many files open may lead to race conditions which occur when multiple processes attempt to modify one file at the same time and can cause all kinds of unexpected behaviors.
The following shows how to call the close() method to close the file:
f.close()Code language: Python (python)To close the file automatically without calling the close() method, you use the with statement like this:
with open(path_to_file) as f: contents = f.readlines()Code language: Python (python)In practice, you’ll use the with statement to close the file automatically.
Reading a text file examples
We’ll use the-zen-of-python.txt file for the demonstration.
The following example illustrates how to use the read() method to read all the contents of the the-zen-of-python.txt file into a string:
with open('the-zen-of-python.txt') as f: contents = f.read() print(contents)Code language: Python (python)Beautiful is better than ugly. Explicit is better than implicit. Simple is better than complex. . Code language: Python (python)The following example uses the readlines() method to read the text file and returns the file contents as a list of strings:
with open('the-zen-of-python.txt') as f: [print(line) for line in f.readlines()]Code language: Python (python)Beautiful is better than ugly. Explicit is better than implicit. Simple is better than complex. Complex is better than complicated. . Code language: Python (python)The reason you see a blank line after each line from a file is that each line in the text file has a newline character (\n). To remove the blank line, you can use the strip() method. For example:
with open('the-zen-of-python.txt') as f: [print(line.strip()) for line in f.readlines()]Code language: Python (python)The following example shows how to use the readline() to read the text file line by line:
with open('the-zen-of-python.txt') as f: while True: line = f.readline() if not line: break print(line.strip())Code language: Python (python)Explicit is better than implicit. Complex is better than complicated. Flat is better than nested. . Code language: Python (python)A more concise way to read a text file line by line
The open() function returns a file object which is an iterable object. Therefore, you can use a for loop to iterate over the lines of a text file as follows:
with open('the-zen-of-python.txt') as f: for line in f: print(line.strip())Code language: Python (python)This is a more concise way to read a text file line by line.
Read UTF-8 text files
The code in the previous examples works fine with ASCII text files. However, if you’re dealing with other languages such as Japanese, Chinese, and Korean, the text file is not a simple ASCII text file. And it’s likely a UTF-8 file that uses more than just the standard ASCII text characters.
To open a UTF-8 text file, you need to pass the encoding=’utf-8′ to the open() function to instruct it to expect UTF-8 characters from the file.
For the demonstration, you’ll use the following quotes.txt file that contains some quotes in Japanese.
The following shows how to loop through the quotes.txt file:
with open('quotes.txt', encoding='utf8') as f: for line in f: print(line.strip())Code language: Python (python)
Summary
- Use the open() function with the ‘r’ mode to open a text file for reading.
- Use the read() , readline() , or readlines() method to read a text file.
- Always close a file after completing reading it using the close() method or the with statement.
- Use the encoding=’utf-8′ to read the UTF-8 text file.