Given a filename and an integer
How to read the first
n lines of the file in your Python script?
Here’s an overview of the solutions:
Method 1: Store Head in a List of Strings
- The expression
next(file)gets the next line of the file.
- The context
for x in range(n)repeats this
Here’s a code script in a file
'code.py' that reads the first
n=4 lines of itself:
n = 4 filename = 'code.py' with open(filename) as my_file: head = [next(my_file) for x in range(n)] print(head)
The output is:
['n = 4\n', "filename = 'code.py'\n", '\n', 'with open(filename) as my_file:\n']
Method 2: Store Head in a String
You can also store the first n lines of a file in a single string using the following idea:
- Create an empty string variable
head = ''
- Open the file with
ntimes using a for loop
- Appending the next line in the file to the end of the string head using string concatenation.
Here’s the specific code:
n = 4 filename = 'code.py' head = '' with open(filename) as my_file: for x in range(n): head += next(my_file) print(head)
print() function gives the following output:
n = 4 filename = 'code.py' head = ''
Method 3: Slicing and readlines()
If performance is not an issue for you, you can read the whole file using the
readlines() function and then use slicing to access only the first
n lines. For example,
file.readlines()[:n] would return a list of the
n first lines in the
n = 4 filename = 'code.py' with open(filename) as file: head = file.readlines()[:n] print(head)
The output of this code snippet is:
['n = 4\n', "filename = 'code.py'\n", '\n', 'with open(filename) as file:\n']
This is not a very performant way to read the head of a file because you first read the whole file before throwing away everything but the first
n lines. Thus, you should only use it if the files are relatively small and you don’t care too much about performance.
Method 4: Pandas
A simple and straightforward solution that doesn’t require explicit file I/O is provided by the pandas library. To read the first
n lines of a file, you can use the pandas call
For example, to read the first five lines of the file
'file.csv', the following two-liner will do:
import pandas as pd head = pd.read_csv('file.csv', nrows=5)
🌍 Recommended Tutorial: How to Read the First Line of a File in Python?
Where to Go From Here?
Enough theory. Let’s get some practice!
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