Pandas TypeError: first argument must be an iterable of pandas objects, you passed an object of type ‘DataFrame’

Updated: February 21, 2024 By: Guest Contributor Post a comment

The Error

The error message ‘Pandas TypeError: first argument must be an iterable of pandas objects, you passed an object of type ‘DataFrame” often occurs when users attempt to concatenate pandas DataFrames incorrectly. The root cause of this error is a violation of the pandas concat function’s requirements. Understanding and resolving this error is crucial for data manipulation in Python. Below are some solutions to address this error, along with their implementation steps and some crucial notes about each approach.

Solution 1: Convert DataFrame to List of DataFrames

If you accidentally pass a DataFrame directly to pd.concat without wrapping it in a list, this error will occur. The solution is simple: convert the DataFrame into a list of DataFrames.

  • Step 1: Assume you have a DataFrame named df.
  • Step 2: Convert df to a list; [df].
  • Step 3: Use pd.concat() to concatenate properly.


# Assuming df is your DataFrame
df_list = [df]
# Concatenating
concatenated_df = pd.concat(df_list)
# Example output


  • This approach is straightforward and works well when you intended to include only one DataFrame in your concatenation process but mistakenly didn’t wrap it in a list.
  • No significant cons if this case applies to your scenario.

Solution 2: Validate Data Structure Before Concatenation

Ensuring that the data structure passed to pd.concat is correct before attempting concatenation can preemptively avoid this error. This method involves checking or transforming your data to the desired format.

  • Step 1: Verify if the object to be concatenated is an iterable of pandas objects. Use isinstance() to check.
  • Step 2: If not in the correct format, transform it (often into a list of DataFrames).
  • Step 3: Perform concatenation.


# Checking if the object is a list containing DataFrames
if not isinstance(data_to_concat, list) or not all(isinstance(df, pd.DataFrame) for df in data_to_concat):
    data_to_concat = [data_to_concat]
# Now concatenate
concatenated_df = pd.concat(data_to_concat)
# Example output


  • This method includes a safety check that can prevent runtime errors and ensure data integrity.
  • The need to add additional checks may increase the code length slightly, but it dramatically enhances error handling.

Solution 3: Using Append Instead of Concat

In some situations, especially when you want to add a single DataFrame to another, using the append method instead of concat might be more appropriate and error-free.

  • Step 1: Assume you have two DataFrames, df1 and df2.
  • Step 2: Use the df1.append(df2) method to combine them without needing to convert them into a list.


# Assuming df1 and df2 are your DataFrames
df_combined = df1.append(df2)
# Example output


  • This method is intuitive and fits scenarios where you are adding rows from one DataFrame to another.
  • append may not be the most efficient manner for large-scale data manipulation due to creating a new object each time it is called, potentially leading to performance issues.


The ‘Pandas TypeError: first argument must be an iterable of pandas objects, you passed an object of type ‘DataFrame” error typically arises from a misuse of the pd.concat function. By understanding the expected input – an iterable of pandas objects – and implementing one of the solutions provided, you can efficiently resolve this error and proceed with data manipulation tasks.