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Top Questions People Ask About Pandas, NumPy, Matplotlib & Scikit-learn — Answered!

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 Whether you're a beginner or brushing up on your skills, these are the real-world questions Python learners ask most about key libraries in data science. Let’s dive in! 🐍 🐼 Pandas: Data Manipulation Made Easy 1. How do I handle missing data in a DataFrame? df.fillna( 0 ) # Replace NaNs with 0 df.dropna() # Remove rows with NaNs df.isna(). sum () # Count missing values per column 2. How can I merge or join two DataFrames? pd.merge(df1, df2, on= 'id' , how= 'inner' ) # inner, left, right, outer 3. What is the difference between loc[] and iloc[] ? loc[] uses labels (e.g., column names) iloc[] uses integer positions df.loc[ 0 , 'name' ] # label-based df.iloc[ 0 , 1 ] # index-based 4. How do I group data and perform aggregation? df.groupby( 'category' )[ 'sales' ]. sum () 5. How can I convert a column to datetime format? df[ 'date' ] = pd.to_datetime(df[ 'date' ]) ...
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Python placeholder '_' Perfect Way to Use it

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What is placeholder in Python? The purpose of it is to mask the variable that you don't want to use in a function. In python, you can call the underscore ( _ ) operator placeholder. Below, you'll find how to use single and double placeholders in a function.


Python placeholder


What is placeholder in python

The purpose of placeholder in Python is to mask variables that you don't want to use in a function. So that your code will be readable. Moreover, in future, if you want to use those variables you can replace the placeholders with the names you want.

In This Page

You'll know in three steps how to use placeholder correctly.
  1. Creating a function
  2. Logic to use single placeholder
  3. Logic to use two placeholders

1. Creating a function.


def function_that_returns_multiple_values(x): 
      return x*2, x*3, x+1 
      for i in range(0,5): 
           square, cube, added_one = function_that_returns_multiple_values(i) 
           print(square, cube)

Here, in print, it returns two variables. I will show you how to mask the unused third variable [added_one] in the below example.

2. Logic to use single placeholder


def function_that_returns_multiple_values(x): 
      return x*2, x*3, x+1 
      for i in range(0,5): 
            square, cube, _ = function_that_returns_multiple_values(i) 
            print(square, cube)

3. Logic to use two placeholders

for i in range(0,5): 
     square, _, _ = function_that_returns_multiple_values(i)


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