Python

Search strings in a file and get line numbers of lines containing the string in Python.

In this article we will discuss how to search strings in a file and get all the lines and line numbers which will match or which contains the string.

Searching string in a file is easily accomplished by python. And we can easily get the line numbers of lines containing the string.

 Check if string is present in file or not  :

First take a file named “example.txt”

This is an example for sample file
Programming needs logic.
Languages are of many types.
Computer science is a study of computers & computational systems.
We can write a program in any language.
The end

Let’s see the program for it.

#Program :

# create a function to check the string is present in the file or not
def string_in_file(file_name, string_to_search):

  #Checking if any line in the metioned file contains given string or not
  # Open the file in read only mode to read content of the file
  with open(file_name, 'r') as read_obj:

  # Reading all lines in the file one by one by iteration
  for line in read_obj:
  # For each line, checking if the line contains the string or not
    if string_to_search in line:
      return True
  return False



#checking if string 'is' is found in file 'sample.txt'
if string_in_file('sample.txt','is'):
  print('string found')
else:
  print('string not found')

Output:
string found

Here, we use loop for iteration to check each line whether the string is present or not. If the line contains the string then it will return True and if the line does not contain the string then it will return False.

Search for a string in file & get all lines containing the string along with line numbers :

Suppose we have a file named “example.txt”

This is an example for sample file
Programming needs logic.
Languages are of many types.
Computer science is a study of computers & computational systems.
We can write a program in any language.
The end

#Program :

def string_in_file(file_name, string_to_search):
    #Searching for the given string in file along with its line numbers
    line_number = 0
    list_of_results = []
    # Opening the file in read only mode
    with open(file_name, 'r') as read_obj:
        # Reading all lines in the file one by one by iterating the file
        for line in read_obj:
            # checking each line, if the line contains the string
            line_number += 1
            if string_to_search in line:
                # If it contains the string, then add the line number & line as a tuple in the list
                list_of_results.append((line_number, line.rstrip()))
    # Return list of tuples containing line numbers and lines where string is found
    return list_of_results


lines = string_in_file('example.txt', 'is')
print('Total Matched lines : ', len(lines))
for i in lines:
    print('Line Number = ', i[0], ' :: Line = ', i[1])

Output:
Total Matched lines : 2
Line Number =  1  :: Line =  This is an example for sample file
Line Number =  4  :: Line =  Computer science is a study of computers & computational systems.

Here, we use loop for iteration to check each line whether the string is present or not. If the line contains the string then it will return True and if the line does not contain the string then it will return False.

We tried to print the total number of matched lines which consist of the string ‘is’. In total, there where two lines, which include the string ‘is’ and this function returned those lines along with their line numbers. Now instead of searching single string we want to search multiple string.

Search for multiple strings in a file and get lines containing string along with the line numbers :

To search for multiple string in a file, we have to create a separate function, that will open a file once and then search for the lines in the file which contains the given string. Because we cannot use the above created function because this will open and close the file for each string.

Suppose we have a file named “example.txt”

This is an example for sample file
Programming needs logic.
Languages are of many types.
Computer science is a study of computers & computational systems.
We can write a program in any language.
The end

#Program :

def strings_in_file(file_name, list_of_strings):
    #Here getting line from the file along with line numbers
    #which contains any of the matching string from the list
    line_number = 0
    list_of_results = []
    # Opening the file in read only mode
    with open(file_name, 'r') as read_obj:
        # Reading all lines in the file one by one by iteration
        for line in read_obj:
            line_number += 1
            # Checking each line, if the line contains any string from the list of strings
            for string_to_search in list_of_strings:
                if string_to_search in line:
                    # If any string is matched/found in line
                    # then we will append that line along with line number in the list
                    list_of_results.append((string_to_search, line_number, line.rstrip()))
    # Returning the list of tuples containing matched string, line numbers and lines where string is found
    return list_of_results

#Now, we will use this function

# search for given strings in the file 'sample.txt'
matched_lines = strings_in_file('sample.txt', ['is', 'what'])
print('Total Matched lines : ', len(matched_lines))
for elem in matched_lines:
    print('Word = ', elem[0], ' :: Line Number = ', elem[1], ' :: Line = ', elem[2])

Output:
Total Matched lines : 2
Word = 'is' :: Line Number =  1  :: Line =  This is an example for sample file
Word = 'is' :: Line Number =  4  :: Line =  Computer science is a study of computers & computational systems.

Here, we use loop for iteration to check each line whether the string is present or not. If the line contains the string then it will return True and if the line does not contain the string then it will return False.

How to convert 2D NumPy array to list of lists in python ?

In this article we will discuss about different ways of converting NumPy array to list of lists in Python. So let’s start exploring the topic.

Converting a 2D Numpy Array to list of lists using tolist() :

In NumPy module of Python, there is a member function tolist() which returns a list congaing the elements of the array. If the array is a 2D array then it returns lists of list.

So, let’s see the implementation of it.

#Program :

import numpy as np
# 2D Numpy array created
arr = np.array([[11, 22, 33, 44],
                [55, 66, 77, 88],
                [12, 13, 23, 43]])

#printing the 2D array                
print(arr)
# Converting 2D Numpy Array to list of lists
list_of_lists = arr.tolist()
#Printing the list of lists
print("The list is")
print(list_of_lists)

Output :
[[11, 22, 33, 44], 
[55, 66, 77, 88], 
[12, 13, 23, 43]]
The list is
[[11, 22, 33, 44], [55, 66, 77, 88], [12, 13, 23, 43]]

Converting a 2D Numpy array to list of lists using iteration :

We can iterate a 2D array row by row and during iteration we can add it to the list. And at the end we can get the list of lists containing all the elements from 2D numpy array.

#Program :

import numpy as np
# 2D Numpy array created
arr = np.array([[11, 22, 33, 44],
                [55, 66, 77, 88],
                [12, 13, 23, 43]])

#printing the 2D array                
print(arr)
# Converting a 2D Numpy Array to list of lists
#iterating row by row using for loop
list_of_lists = list()
for row in arr:
    list_of_lists.append(row.tolist())
#Printing the list of lists
print("The list is")
print(list_of_lists)

Output :
[[11, 22, 33, 44], 
[55, 66, 77, 88], 
[12, 13, 23, 43]]
The list is
[[11, 22, 33, 44], [55, 66, 77, 88], [12, 13, 23, 43]]

Converting a 2D Numpy Array to a flat list :

In both the example, we observed that a 2D NumPy array converted into list of lists. But we can also convert it into a  flat list (not a list of lists) . So, for that first we can convert the 2D NumPy array into 1D Numpy array by using flatten() method.. Then call the tolist() function to convert it into flat list.

#Program :

import numpy as np
# 2D Numpy array created
arr = np.array([[11, 22, 33, 44],
                [55, 66, 77, 88],
                [12, 13, 23, 43]])

#printing the 2D array                
print(arr)

# Converting 2D Numpy array to a flat list
my_list = arr.flatten().tolist()
#Printing the list of lists
print("The list is")
print(my_list)

Output :
[[11, 22, 33, 44], 
[55, 66, 77, 88], 
[12, 13, 23, 43]] 
The list is [11, 22, 33, 44, 55, 66, 77, 88, 12, 13, 23, 43]

Three ways to check if a file is empty in Python.

This article is about to check if a file is empty in Python. We will use three different ways to check if a file is empty or not.

The three ways are

1. Using os.stat() method.
2. Using  os.path.getsize() method.
3. Reading its first character.

Method-1 : Use os.stat() to check if a file is empty :

In python, there is a stat() function which can be used to get the statistics about a file.

os.stat(path, *, dir_fd=None, follow_symlinks=True)

This function

• It accepts file path (string type) as an argument.
• It returns an object of the structure stat containing various attributes. (Like st.size to know size of the file)

#Program :

#importing the os module
import os

#file path as string type
path_of_file = 'sample.txt'

# checking if size of file is 0
if os.stat(path_of_file).st_size == 0:
    print('File is empty')
else:
    print('File is not empty')

Output :
File is empty

As our file is empty, so it returned ‘File is empty’.

But we have to be more careful while using it, because if the file does not exist at the respective path then FileNotFoundError.

FileNotFoundError: [WinError 2] The system cannot find the file specified: FILE_NAME

So by keeping that in mind first we will check the file exists or not. We will create a separate function for that. After checking if we will find the file exists then we will check the file is empty or not.

So, let’s see the implementation of it.

#Program :

import os

#Checking the file exists or not
def check_file_empty(path_of_file):
    #Checking if file exist and it is empty
    return os.path.exists(path_of_file) and os.stat(path_of_file).st_size == 0

path_of_file = 'sample.txt'

# checking if file exist and it is empty
EmptyOrNot = check_file_empty(path_of_file)
if EmptyOrNot:
    print('File is empty')
else:
    print('File is not empty')

Output :
File is empty

Method-2 : Check if file is empty using os.path.getsize() in Python :

In Python, os module there is an another function, by using which we can check if a file is empty or not.

os.path.getsize(path)

This function takes file path as an argument and returns the size in bytes. If the file does not exists it gives FileNotFoundError.

#program :

import os

#file path
path_of_file = 'sample.txt'

# checking if size of file is 0
if os.path.getsize(path_of_file) == 0:
    print('File is empty')
else:
    print('File is not empty')

Output : 
File is empty

Method-3 : Check if the file is empty by reading its first character in Python :

We can also check a file is empty or not by reading first character of the file. So, for that it opens the file in read only mode. Then it tries to read first character of the string. If it finds first character in the file then file exists and if it does not find the first character then the file is empty.

#Program :

def file_empty(file_name):
    # open file in read mode
    # Reading first character to check file is empty or not
    with open(file_name, 'r') as read_obj:
        # reading the first character
        one_char = read_obj.read(1)
        # if first character not fpound then file is empty
        if not one_char:
           return True
    return False

path_of_file = 'mysample.txt'
# check if file is empty
EmptyOrNot = file_empty(path_of_file)
print(EmptyOrNot)

Output : 
File is empty

Count all rows or those that satisfy some condition in Pandas dataframe

In this article we are going to show you how to count number of all rows in a DataFrame or rows that satisfy given condition in it.

First we are going to create dataframe,

import pandas as pd
students = [('Ankit', 22, 'Up', 'Geu'),
           ('Ankita', 31, 'Delhi', 'Gehu'),
           ('Rahul', 16, 'Tokyo', 'Abes'),
           ('Simran', 41, 'Delhi', 'Gehu'),
           ('Shaurya', 33, 'Delhi', 'Geu'),
           ('Harshita', 35, 'Mumbai', 'Bhu' ),
           ('Swapnil', 35, 'Mp', 'Geu'),
           ('Priya', 35, 'Uk', 'Geu'),
           ('Jeet', 35, 'Guj', 'Gehu'),
           ('Ananya', 35, 'Up', 'Bhu')
            ]
details = pd.DataFrame(students, columns =['Name', 'Age','Place', 'College'],
          index =['a', 'b', 'c', 'd', 'e','f', 'g', 'i', 'j', 'k'])

print(details)

Output:

RESTART: C:/Users/HP/Desktop/dataframe.py
Name       Age   Place      College
a   Ankit         22     Up          Geu
b   Ankita       31    Delhi       Gehu
c    Rahul       16    Tokyo      Abes
d   Simran     41     Delhi      Gehu
e   Shaurya    33     Delhi      Geu
f    Harshita   35     Mumbai Bhu
g   Swapnil    35     Mp        Geu
i    Priya         35     Uk         Geu
j    Jeet          35     Guj        Gehu
k   Ananya     35    Up         Bhu

Now lets see some other methods to count the rows in dataframe.

Count all rows in a Pandas Dataframe using Dataframe.shape

Dataframe.shape attribute gives a sequence of index or row labels

(Number_of_index, Number_of_columns)

Number of index basically means number of rows in the dataframe.Let’s use this to count number of rows in above created dataframe.

import pandas as pd
students = [('Ankit', 22, 'Up', 'Geu'),
           ('Ankita', 31, 'Delhi', 'Gehu'),
           ('Rahul', 16, 'Tokyo', 'Abes'),
           ('Simran', 41, 'Delhi', 'Gehu'),
           ('Shaurya', 33, 'Delhi', 'Geu'),
           ('Harshita', 35, 'Mumbai', 'Bhu' ),
           ('Swapnil', 35, 'Mp', 'Geu'),
           ('Priya', 35, 'Uk', 'Geu'),
           ('Jeet', 35, 'Guj', 'Gehu'),
           ('Ananya', 35, 'Up', 'Bhu')
            ]
details = pd.DataFrame(students, columns =['Name', 'Age','Place', 'College'],
          index =['a', 'b', 'c', 'd', 'e','f', 'g', 'i', 'j', 'k'])
numOfRows = details.shape[0]

print("Number of rows :",numOfRows)

Output:

RESTART: C:/Users/HP/Desktop/dataframe.py
Number of rows : 10

Count all rows in a Pandas Dataframe using Dataframe.index

Dataframe.index attribute gives a sequence of index or row labels.We can calculate the length of that sequence to find out the number of rows in the dataframe.

import pandas as pd
students = [('Ankit', 22, 'Up', 'Geu'),
           ('Ankita', 31, 'Delhi', 'Gehu'),
           ('Rahul', 16, 'Tokyo', 'Abes'),
           ('Simran', 41, 'Delhi', 'Gehu'),
           ('Shaurya', 33, 'Delhi', 'Geu'),
           ('Harshita', 35, 'Mumbai', 'Bhu' ),
           ('Swapnil', 35, 'Mp', 'Geu'),
           ('Priya', 35, 'Uk', 'Geu'),
           ('Jeet', 35, 'Guj', 'Gehu'),
           ('Ananya', 35, 'Up', 'Bhu')
            ]
details = pd.DataFrame(students, columns =['Name', 'Age','Place', 'College'],
          index =['a', 'b', 'c', 'd', 'e','f', 'g', 'i', 'j', 'k'])
numOfRows = len(details.index)
print('Number of Rows in dataframe : ' , numOfRows)

Output:

RESTART: C:/Users/HP/Desktop/dataframe.py

Number of rows : 10

Count rows in a Pandas Dataframe that satisfies a condition using Dataframe.apply()

This function apply  to all the rows of a dataframe to find out if elements of rows satisfies a condition or not, Based on the result it returns a bool series.

import pandas as pd
students = [('Ankit', 22, 'Up', 'Geu'),
           ('Ankita', 31, 'Delhi', 'Gehu'),
           ('Rahul', 16, 'Tokyo', 'Abes'),
           ('Simran', 41, 'Delhi', 'Gehu'),
           ('Shaurya', 33, 'Delhi', 'Geu'),
           ('Harshita', 35, 'Mumbai', 'Bhu' ),
           ('Swapnil', 35, 'Mp', 'Geu'),
           ('Priya', 35, 'Uk', 'Geu'),
           ('Jeet', 35, 'Guj', 'Gehu'),
           ('Ananya', 35, 'Up', 'Bhu')
            ]
details = pd.DataFrame(students, columns =['Name', 'Age','Place', 'College'],
          index =['a', 'b', 'c', 'd', 'e','f', 'g', 'i', 'j', 'k'])
seriesObj = details.apply(lambda x: True if x['Age'] > 30 else False , axis=1)
numOfRows = len(seriesObj[seriesObj == True].index)
print('Number of Rows in dataframe in which Age > 30 : ', numOfRows)

Output:

RESTART: C:/Users/HP/Desktop/dataframe.py
Number of Rows in dataframe in which Age > 30 : 8

Want to expert in the python programming language? Exploring Python Data Analysis using Pandas tutorial changes your knowledge from basic to advance level in python concepts.

Read more Articles on Python Data Analysis Using Padas

• How to merge Dataframes using Dataframe.merge() in Python?
• How to merge Dataframes on specific columns or on index in Python?
• How to merge Dataframes by index using Dataframe.merge()?
• Count NaN or missing values in DataFrame
• 6 Different ways to iterate over rows in a Dataframe & Update while iterating row by row
• Loop or Iterate over all or certain columns of a DataFrame
• How to display full Dataframe i.e. print all rows & columns without truncation

Conclusion:

In this article we have seen different method to count rows in a dataframe  all or those  that satisfy a condition.

Happy learning guys.