keyerror python tutorial

understanding keyerror in python

in python, a `keyerror` is raised when you try to access a dictionary with a key that does not exist. this is a common exception when working with dictionaries (hash maps) in python, and it can also occur when trying to access keys in a pandas dataframe.

basic dictionary example

let's start by looking at a simple example of `keyerror` using a python dictionary.

```python
example of keyerror with a dictionary

define a dictionary
my_dict = {
'name': 'alice',
'age': 30,
'city': 'new york'
}

trying to access a key that exists
print(my_dict['name']) output: alice

trying to access a key that does not exist
try:
print(my_dict['country']) this will raise a keyerror
except keyerror as e:
print(f"keyerror: {e}")
```

**explanation:**
1. we defined a dictionary `my_dict` with three keys: `'name'`, `'age'`, and `'city'`.
2. when we try to access `my_dict['country']`, it raises a `keyerror` because `'country'` is not a key in the dictionary.
3. we catch the exception using a `try-except` block and print a user-friendly message.

preventing keyerror

you can prevent `keyerror` by using one of the following methods:

1. **using the `get()` method:**
the `get()` method of a dictionary allows you to specify a default value if the key does not exist.

```python
using get() to avoid keyerror
print(country) output: not available
```

2. **using the `in` keyword:**
you can check if a key exists in the dictionary before trying to access it.

```python
checking if a key exists before accessing it
if 'country' in my_dict:
print(my_dict['country'])
else:
print("key 'country' does not exist.")
```

using keyerror with pandas

when working with pandas dataframes, you may encounter `keyerror` when trying to access a column that does not exist.

```python
import pandas as pd

create a sample dataframe
data = {
'name': ['alice', 'bob', 'charlie'],
' ...

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