TypeError: merge() Missing 'right' Argument in Pandas

The error 'TypeError: merge() missing 1 required positional argument: 'right'' in pandas indicates that the merge() function needs two parameters: left and right. You need to provide two DataFrame objects as arguments to perform the merge operation.

Example:

import pandas as pd

# Create two DataFrames
left_df = pd.DataFrame({'key': ['A', 'B', 'C'], 'value1': [1, 2, 3]})
right_df = pd.DataFrame({'key': ['A', 'C', 'D'], 'value2': [4, 5, 6]})

# Perform the merge operation
merged_df = pd.merge(left_df, right_df, on='key')

# Print the merged DataFrame
print(merged_df)

In this example, left_df and right_df are the two DataFrames being merged based on the common column 'key'.

Common Causes of the Error:

• Missing 'right' argument: You may have forgotten to provide the second DataFrame as the right argument.
• Incorrect data type: The left and right arguments should be pandas DataFrames.

Solution:

Ensure that you provide both the left and right DataFrames as arguments to the merge() function. Make sure they are both valid pandas DataFrames.

Example with error:

import pandas as pd

# Create two DataFrames
left_df = pd.DataFrame({'key': ['A', 'B', 'C'], 'value1': [1, 2, 3]})

# Missing 'right' argument
merged_df = pd.merge(left_df, on='key') # Error: merge() missing 1 required positional argument: 'right'

# Print the merged DataFrame
print(merged_df)

Example with fix:

import pandas as pd

# Create two DataFrames
left_df = pd.DataFrame({'key': ['A', 'B', 'C'], 'value1': [1, 2, 3]})
right_df = pd.DataFrame({'key': ['A', 'C', 'D'], 'value2': [4, 5, 6]})

# Perform the merge operation
merged_df = pd.merge(left_df, right_df, on='key')

# Print the merged DataFrame
print(merged_df)