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Using pandas and bs4 for web scrapping.

By David Li on Fri, 14 August 2024

Pandas is an open-source Python library used for data manipulation and analysis. It is a powerful tool for handling structured data, such as spreadsheets and SQL tables. One of the most useful features of pandas is its ability to read and write data from various file formats, including CSV, Excel, and SQL databases.

Pandas can also be used for web scraping by reading data from HTML tables on web pages. The library provides a method called read_html() that can parse HTML tables and return a list of data frames. Data frames are two-dimensional tables with labeled rows and columns, similar to spreadsheets.

Here’s an example code snippet that uses pandas to scrape a table from a web page:

import pandas as pd

# URL of the web page containing the table
url = 'https://www.example.com/table.html'

# Read the HTML table into a list of data frames
dfs = pd.read_html(url)

# Extract the first data frame (assuming only one table on the page)
df = dfs[0]

# Print the first 5 rows of the data frame
print(df.head())

In this code snippet, we first import the pandas library using the import statement. We then specify the URL of the web page containing the table we want to scrape. We use the pd.read_html() method to read the HTML table into a list of data frames. Since read_html() can potentially return multiple data frames (if there are multiple tables on the page), we extract the first data frame using the index [0]. Finally, we print the first 5 rows of the data frame using the head() method.

Note that read_html() can handle some simple HTML tables, but may not work with more complex tables or tables that are embedded within other elements on the page. In such cases, we may need to use other web scraping techniques or libraries.

Overall, pandas is a powerful tool for web scraping and data analysis, and can save us a lot of time and effort when working with structured data on the web.

Beautiful Soup (bs4) is a Python library used for web scraping. It allows us to parse HTML and XML documents and extract information from them. One common use case for bs4 is to scrape data from tables on web pages.

To extract the data from a table using bs4, we first need to obtain the HTML source code of the web page containing the table. We can do this using the requests library, which allows us to make HTTP requests to web pages and retrieve their HTML content. Here’s an example code snippet that shows how to get the HTML source code of a web page:

import requests

# URL of the web page we want to scrape
url = 'https://www.example.com/table.html'

# Make a GET request to the URL and get the HTML content
response = requests.get(url)
html_content = response.content

# Print the HTML content
print(html_content)

In this code snippet, we first import the requests library using the import statement. We then specify the URL of the web page we want to scrape. We use the requests.get() method to make a GET request to the URL and retrieve the HTML content. We store the content in a variable called html_content and print it to the console.

Once we have the HTML source code of the web page, we can use bs4 to extract the table data. We start by creating a BeautifulSoup object and passing in the HTML content. We can then use the find() or find_all() methods to locate the table element(s) and extract their data. Here’s an example code snippet that shows how to extract the data from a table using bs4:

from bs4 import BeautifulSoup

# Create a BeautifulSoup object and pass in the HTML content
soup = BeautifulSoup(html_content, 'html.parser')

# Find the first table element on the page
table = soup.find('table')

# Loop through the rows of the table and extract the data
for row in table.find_all('tr'):
 # Extract the data from each cell in the row
 cells = row.find_all('td')
 data = [cell.text.strip() for cell in cells]
 
 # Print the data for this row
 print(data)

In this code snippet, we first import the BeautifulSoup class from the bs4 library. We create a soup object by passing in the HTML content and specifying the parser to use (in this case, the built-in html.parser).

We then use the soup.find() method to find the first table element on the page. We can use the find_all() method to find all table elements on the page.

Next, we loop through the rows of the table using the find_all('tr') method. For each row, we extract the data from each cell using the find_all('td') method, which finds all td elements in the row. We then use a list comprehension to extract the text content of each cell and strip any whitespace using the text.strip() method.

Finally, we print the data for each row to the console. Note that this code snippet assumes that the table contains only text data. If the table contains other types of elements, such as links or images, we may need to modify the code to handle those cases.

Overall, bs4 is a powerful tool for web scraping, and can save us a lot of time and effort when working with HTML documents.

Pandas is a popular Python library for data analysis, manipulation, and cleaning. It is often used in data science projects, including web scraping, to process and analyze data in a tabular format.

To parse a table using pandas, we first need to obtain the HTML source code of the web page containing the table. We can do this using the requests library, as shown in the previous example. Once we have the HTML source code, we can use the read_html() method provided by pandas to parse the table data. Here’s an example code snippet that shows how to extract the data from a table using pandas:

import pandas as pd

# URL of the web page we want to scrape
url = 'https://www.example.com/table.html'

# Use pandas to read the table data from the URL
tables = pd.read_html(url)

# Print the first table
print(tables[0])

In this code snippet, we first import the pandas library using the import statement. We then specify the URL of the web page we want to scrape. We use the pd.read_html() method to read the table data from the URL and store the result in a variable called tables. This method returns a list of DataFrame objects, one for each table on the page.

In this example, we assume that the page contains only one table, so we print the first table using print(tables[0]). If the page contains multiple tables, we can print each table by looping through the list of DataFrame objects.

Pandas also provides several methods for manipulating and cleaning the data in the DataFrame objects. For example, we can use the drop() method to remove columns or rows with missing data, the fillna() method to fill in missing data with a default value, or the merge() method to combine multiple DataFrame objects into a single object.

Overall, pandas is a powerful tool for working with tabular data and can simplify the process of extracting and processing data from web pages.

Once we have parsed the table using pandas, we can easily output it to a CSV (comma-separated values) file using the to_csv() method provided by pandas. Here’s an example code snippet that shows how to output the table to a CSV file:

import pandas as pd

# URL of the web page we want to scrape
url = 'https://www.example.com/table.html'

# Use pandas to read the table data from the URL
tables = pd.read_html(url)

# Get the first table from the list
df = tables[0]

# Output the table to a CSV file
df.to_csv('table.csv', index=False)

In this code snippet, we first import the pandas library using the import statement. We then specify the URL of the web page we want to scrape and use pd.read_html() to read the table data from the URL and store it in the tables variable.

Next, we get the first table from the tables list and store it in a variable called df. We then use the to_csv() method to output the table to a CSV file called table.csv. The index=False parameter tells pandas not to include the row index numbers in the output file.

Once the code is executed, a CSV file called table.csv will be created in the current working directory with the data from the table. We can open this file in any spreadsheet application, such as Excel or Google Sheets, to view and manipulate the data further.

Overall, pandas makes it easy to output table data to a variety of file formats, including CSV, Excel, and SQL databases. This flexibility makes it a popular choice for data scientists and analysts who need to work with data from a variety of sources.

Pandas is a powerful library that provides many advanced features for cleaning and manipulating data. In this section, we’ll explore some of these features that can be used to clean the data extracted from a website.

  1. Removing Duplicates: Sometimes a web page might have duplicate rows in its table, which can cause problems in our data analysis. Pandas provides a drop_duplicates() method to remove duplicate rows from a DataFrame. Here’s an example code snippet:
import pandas as pd

# URL of the web page we want to scrape
url = 'https://www.example.com/table.html'

# Use pandas to read the table data from the URL
tables = pd.read_html(url)

# Get the first table from the list
df = tables[0]

# Drop duplicate rows
df.drop_duplicates(inplace=True)

In this example, we first parse the table using pandas and get the first table from the list of DataFrame objects. We then use the drop_duplicates() method to remove any duplicate rows in the table. The inplace=True parameter tells pandas to modify the DataFrame in place rather than returning a new DataFrame object.

  1. Renaming Columns: The column names in a table might not always be in a format that’s suitable for our data analysis. Pandas provides a rename() method to change the column names of a DataFrame. Here’s an example code snippet:
import pandas as pd

# URL of the web page we want to scrape
url = 'https://www.example.com/table.html'

# Use pandas to read the table data from the URL
tables = pd.read_html(url)

# Get the first table from the list
df = tables[0]

# Rename the columns
df = df.rename(columns={'old\_column\_name': 'new\_column\_name'})

In this example, we first parse the table using pandas and get the first table from the list of DataFrame objects. We then use the rename() method to change the name of a specific column in the DataFrame. The {'old_column_name': 'new_column_name'} parameter tells pandas to replace the old column name with the new column name.

  1. Dealing with Missing Values: Web pages might have missing data in their tables, which can cause problems in our data analysis. Pandas provides several methods for dealing with missing values, including the dropna() and fillna() methods.

The dropna() method removes any rows or columns with missing values from a DataFrame, while the fillna() method fills in the missing values with a default value or a value calculated from the other data in the DataFrame.

Here’s an example code snippet:

import pandas as pd

# URL of the web page we want to scrape
url = 'https://www.example.com/table.html'

# Use pandas to read the table data from the URL
tables = pd.read_html(url)

# Get the first table from the list
df = tables[0]

# Remove rows with missing data
df = df.dropna()

# Fill in missing data with a default value
df = df.fillna(0)

In this example, we first parse the table using pandas and get the first table from the list of DataFrame objects. We then use the dropna() method to remove any rows with missing data from the DataFrame. We then use the fillna() method to fill in any remaining missing data with the value 0.

Overall, pandas provides a wide range of features for cleaning and manipulating data, which makes it a popular choice for data scientists and analysts. By using these advanced features, we can transform raw data extracted from a website into a format that’s suitable for our data analysis.

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