Use sep=r'\s*,\s*' to parse a file where the columns may have some number of spaces preceding or following the delimiter (e.g. , ):

transactions = pd.read_csv('transactions.csv', sep=r'\s*,\s*',
                           header=0, encoding='ascii', engine='python')

Prove:

print(transactions.columns)

Output:

Index(['product_id', 'customer_id', 'store_id', 'promotion_id', 'month_of_year', 'quarter', 'the_year', 'store_sales', 'store_cost', 'unit_sales', 'fact_count'], dtype='object')

Alternatively, remove unquoted spaces in the CSV file, and use your command (unchanged).

Answer from MaxU - stand with Ukraine on Stack Overflow
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GeeksforGeeks
geeksforgeeks.org › python › how-to-fix-keyerror-in-pandas
How to Fix: KeyError in Pandas - GeeksforGeeks
July 23, 2025 - Pandas KeyError occurs when you try to access a column or row label in a DataFrame that doesn’t exist. This error often results from misspelled labels, unwanted spaces, or case mismatches.
Discussions

Dataframe output Key Error
Can you share a screenshot of what the dataframe looks like before you write it? Better to show the output of a Jupyter Notebook cell, as opposed to printing it · According to the error, it looks like there's an issue with the loop's range. However, if you are able to print the Dataframe, ... More on community.alteryx.com
🌐 community.alteryx.com
July 13, 2022
Key error in pandas
You have a bracket problem, when you call data by loc , call data.loc[[indexX],[indexY1,indexY2]] enclose everything in brackets and close the X index bract. More on reddit.com
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5
0
September 13, 2025
python - Pandas - Getting a Key Error when the Key Exists - Stack Overflow
I'm trying to join two dataframes in Pandas. The first frame is called Trades and has these columns: TRADE DATE ACCOUNT COMPANY COST CENTER CURRENCY The second frame is called Company_Mapping an... More on stackoverflow.com
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Help with understanding why Pandas is KeyError-ing
I'm working on this same program and having this problem as well This problem only happened for me when I deleted the "[:1]" on the end of the for loop in order to display all 500 stocks instead of the first batch of 100 for symbol_string in symbol_strings[:1]: The problem only occurred after I get rid of the [:1] More on reddit.com
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19
10
April 16, 2022
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Medium
medium.com › @heyamit10 › how-to-fix-pandas-keyerror-step-by-step-solutions-a225760b227c
How to Fix Pandas KeyError? (Step-by-Step Solutions) | by Hey Amit | Medium
April 18, 2025 - This prevents KeyError by checking first before accessing. A simple yet effective fix! ... You might be wondering: “Can I access a column without causing an error?” Yes, you can! ... ✅ If the column exists, it prints the data. ❌ If not, it gracefully returns a default message instead of breaking your code. ... Pandas is case-sensitive, so "Name" and "name" are not the same.
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LearnDataSci
learndatasci.com › solutions › python-keyerror
Python KeyError: How to fix and avoid key errors – LearnDataSci
KeyError occurs when searching for a key that does not exist. Dictionaries, Pandas Series, and DataFrames can trigger this error.
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Kanaries
docs.kanaries.net › topics › Pandas › key-errors-in-pandas
Pandas KeyError: Column Not Found — How to Fix It (Even When Column Exists)
A KeyError in pandas means you tried to access a column (or index label) that pandas cannot find in the DataFrame. The full error looks like this:
Find elsewhere
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Zerve
zerve.ai › data-science-problems › pandas › keyerror-column-not-found-fix
Fix Pandas KeyError: Column Not Found
The rule: when you hit a KeyError, run df.columns.tolist() immediately to see what's actually there. pythonimport pandas as pd df = pd.DataFrame({'product_name': ['A', 'B'], 'price': [10, 20]}) # ❌ Problematic: column name doesn't exist df['product'] # KeyError: 'product' # ✅ Fixed: check columns first, use correct name print(df.columns.tolist()) # ['product_name', 'price'] df['product_name'] # ✅ Strip whitespace from column names if that's the issue df.columns = df.columns.str.strip()
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Saturn Cloud
saturncloud.io › blog › how-to-handle-pandas-keyerror-value-not-in-index
How to Handle Pandas KeyError Value Not in Index | Saturn Cloud Blog
May 1, 2026 - The Pandas KeyError occurs when a key (e.g., a column or index label) is not found in a DataFrame or Series. This error can occur for several reasons, such as:
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Alteryx Community
community.alteryx.com › t5 › Alteryx-Designer-Desktop-Discussions › Dataframe-output-Key-Error › td-p › 968249
Solved: Dataframe output Key Error - Alteryx Community
October 23, 2023 - According to the error, it looks like there's an issue with the loop's range. However, if you are able to print the Dataframe, but not write it (assuming all else is equal), this wouldn't make sense. Is there any way you can provide the data set so I can investigate further? ... Pandas KeyError occurs when we try to access some column/row label in our DataFrame that doesn’t exist.
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Reddit
reddit.com › r/learnpython › help with understanding why pandas is keyerror-ing
r/learnpython on Reddit: Help with understanding why Pandas is KeyError-ing
April 16, 2022 -

Hi all, I'm trying my best to grok this and it's just not working.

I'm following along with a tutorial and am hitting a problem with a Pandas append.

Here's the code blob where it's breaking:

def chunks(lst, n):
    """Yield successive n-sized chunks from lst."""
    for i in range(0, len(lst), n):
        yield lst[i:i + n]

my_columns = ['Ticker','Stock Price', 'Market Capitalization', 'Number of Shares to Buy']
symbol_groups = list(chunks(stocks['Ticker'], 100))
symbol_strings = []

final_dataframe = pd.DataFrame(columns = my_columns)

for symbol_string in symbol_strings:
    batch_api_call_url = f'https://sandbox.iexapis.com/stable/stock/market/batch?symbols={symbol_string}&types=quote&token={IEX_CLOUD_API_TOKEN}'
    data = requests.get(batch_api_call_url).json()
    for symbol in symbol_string.split(','):
        final_dataframe = final_dataframe.append(
            pd.Series(
                [symbol,
                data[symbol]['quote']['latestPrice'],
                data[symbol]['quote']['marketCap'],
                'N/A'],
            index = my_columns),
        ignore_index=True)

final_dataframe

Calling the dataframe gives me a KeyError: 'DISCA' pointing at the call to the data[symbol]['quote']['latestPrice'].

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
C:\Users\blahblahblah/ipykernel_19420/1231875517.py in <module>
     15             pd.Series(
     16                 [symbol,
---> 17                 data[symbol]['quote']['latestPrice'],
     18                 data[symbol]['quote']['marketCap'],
     19                 'N/A'],

KeyError: 'DISCA'

This seems wonky to me, because I can print(data[symbol]['quote']['latestPrice']) and see the results no problem. I can print(data[symbol]) and get all my symbols no problem... I know the data is there, but Pandas can't seem to append it in for some reason.

I know it's a simple fix because I was stupidly doing edits and got it working, then backtracked through a bunch of changes to see what did it and broke it again, coz I'm dumb.

Edit: Also, the 'solved' workbook has the same issue - so I can't just go compare code for the fix. =
Edit2: Ok, backtracing the problem some more:

for symbol_string in symbol_strings:
    batch_api_call_url = f'https://sandbox.iexapis.com/stable/stock/market/batch/?types=quote&symbols={symbol_string}&token={IEX_CLOUD_API_TOKEN}'
    data = requests.get(batch_api_call_url).json()
    print(data['A'])

This will print 'A' and all of it's data, however it will still throw a keyerror out:

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
C:\Users\blahblahblah/ipykernel_11588/3831869600.py in <module>
     12     data = requests.get(batch_api_call_url).json()
     13     #print(data[A])
---> 14     print(data['A'])

KeyError: 'A'

Sooo this is happening above this part of the blob... I think?

Edit3:

u/Available_Net_9341 has found the answer - delisted tickers that were breaking the for loop.

🌐
GitHub
github.com › pandas-dev › pandas › issues › 42530
BUG: `KeyError` when assigning to Series values after pop from DataFrame · Issue #42530 · pandas-dev/pandas
July 14, 2021 - 3897 """ -> 3898 loc = self._info_axis.get_loc(item) 3899 arraylike = value._values 3900 self._mgr.iset(loc, arraylike) ~/.envs/sigma/lib/python3.8/site-packages/pandas/core/indexes/base.py in get_loc(self, key, method, tolerance) 3361 return self._engine.get_loc(casted_key) 3362 except KeyError as err: -> 3363 raise KeyError(key) from err 3364 3365 if is_scalar(key) and isna(key) and not self.hasnans: KeyError: 'b'
Author   pandas-dev
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Statology
statology.org › home › how to fix keyerror in pandas (with example)
How to Fix KeyError in Pandas (With Example)
August 6, 2021 - One error you may encounter when using pandas is: KeyError: 'column_name' This error occurs when you attempt to access some column in a pandas DataFrame that does not exist. Typically this error occurs when you simply misspell a column names ...
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Medium
medium.com › @shivamkaus › how-to-fix-pandas-keyerror-0-pythonpandas-04a4a105acac
How to fix Pandas keyerror: 0 — PythonPandas | by Shivam Kau | Medium
June 29, 2025 - The KeyError: 0 in Pandas typically occurs when you’re trying to access a column or index that does not exist in the DataFrame. In most cases, this error happens when you try to access a non-existent column by using an integer as the key, or when you’re trying to access a row or index that ...
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GitHub
github.com › pandas-dev › pandas › issues › 58474
BUG: Unexpected KeyError in `transform()` with dict-like func argument · Issue #58474 · pandas-dev/pandas
April 29, 2024 - ApplyApply, Aggregate, Transform, MapApply, Aggregate, Transform, MapError ReportingIncorrect or improved errors from pandasIncorrect or improved errors from pandas ... I have checked that this issue has not already been reported. I have confirmed this bug exists on the latest version of pandas. I have confirmed this bug exists on the main branch of pandas. import pandas as pd pd.DataFrame({'foo': [2,4,6], 'bar': [1,2,3]}).transform( { 'foo': lambda x: x+2, 'bar': lambda x: x*2 }, axis="columns" ) The code raises KeyError: "Column(s) ['bar', 'foo'] do not exist" even though the columns are present, evidently.
Author   pandas-dev
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Statology
statology.org › home › how to fix in pandas: keyerror: “[‘label’] not found in axis”
How to Fix in Pandas: KeyError: "['Label'] not found in axis"
November 23, 2021 - This error usually occurs when you attempt to drop a column from a pandas DataFrames and forget to specify axis=1.