chore: import upstream snapshot with attribution
This commit is contained in:
wehub-resource-sync
@@ -0,0 +1,593 @@
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# Python Error Patterns
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Common Python errors with diagnosis and solutions.
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## Import Errors
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### ModuleNotFoundError
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```python
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ModuleNotFoundError: No module named 'package_name'
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```
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**Causes**:
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1. Package not installed
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2. Virtual environment not activated
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3. Wrong Python version
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4. Typo in module name
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**Diagnosis**:
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```bash
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# Check if package installed
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pip show package_name
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pip list | grep package
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# Check which Python
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which python
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python --version
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# Check if in venv
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echo $VIRTUAL_ENV
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```
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**Solutions**:
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```bash
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# Install package
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pip install package_name
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# If using virtual env
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source venv/bin/activate
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pip install package_name
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# If wrong Python version
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python3 -m pip install package_name
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pip3 install package_name
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```
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---
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### ImportError: cannot import name 'X' from 'Y'
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```python
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ImportError: cannot import name 'MyClass' from 'mymodule'
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```
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**Causes**:
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1. Name doesn't exist in module
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2. Circular import
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3. Module structure changed
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4. Typo in name
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**Diagnosis**:
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```python
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# Check what's available
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import mymodule
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print(dir(mymodule))
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# Check if circular import
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# Add print at top of each module to see import order
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```
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**Solutions**:
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```python
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# Circular import fix - move import inside function
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def my_function():
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from other_module import something
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return something()
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# Or restructure to avoid circular dependency
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```
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---
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## Type Errors
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### TypeError: 'NoneType' object is not subscriptable
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```python
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TypeError: 'NoneType' object is not subscriptable
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```
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**Causes**:
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1. Function returned None (forgot return)
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2. dict.get() returned None
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3. API response is None
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**Solutions**:
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```python
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# Add None check
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if result is not None:
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value = result['key']
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# Use default value
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value = result.get('key', 'default') if result else 'default'
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# Use walrus operator (Python 3.8+)
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if (result := get_result()) is not None:
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value = result['key']
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```
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---
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### TypeError: 'X' object is not callable
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```python
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TypeError: 'str' object is not callable
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```
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**Causes**:
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1. Variable shadows built-in function
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2. Missing method parentheses somewhere
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3. Property accessed as method
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**Common Culprits**:
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```python
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# Shadowing built-ins - DON'T DO THIS
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list = [1, 2, 3] # Shadows list()
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str = "hello" # Shadows str()
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dict = {'a': 1} # Shadows dict()
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type = "my_type" # Shadows type()
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id = 123 # Shadows id()
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```
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**Solutions**:
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```python
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# Rename variables
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my_list = [1, 2, 3]
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my_str = "hello"
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# Or delete the shadow
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del list
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```
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---
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### TypeError: unsupported operand type(s)
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```python
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TypeError: unsupported operand type(s) for +: 'int' and 'str'
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```
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**Causes**:
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1. Mixing types in operation
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2. Unexpected type from input/API
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**Solutions**:
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```python
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# Convert types explicitly
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result = str(number) + text
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result = number + int(text)
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# Type checking
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if isinstance(value, int):
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result = value + 10
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```
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---
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## Attribute Errors
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### AttributeError: 'NoneType' object has no attribute 'X'
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```python
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AttributeError: 'NoneType' object has no attribute 'split'
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```
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**Causes**:
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1. Variable is None when it shouldn't be
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2. Function returned None
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3. Failed assignment
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**Solutions**:
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```python
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# Guard against None
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if text is not None:
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words = text.split()
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# With default
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words = (text or "").split()
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# Assert early
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assert text is not None, "text cannot be None"
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```
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---
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### AttributeError: module 'X' has no attribute 'Y'
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```python
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AttributeError: module 'json' has no attribute 'loads'
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```
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**Causes**:
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1. Local file shadows standard library
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2. Wrong module imported
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3. Outdated module version
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**Diagnosis**:
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```python
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import json
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print(json.__file__) # Check which file is loaded
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```
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**Solutions**:
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```bash
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# If local file shadows stdlib
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mv json.py my_json_utils.py
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rm json.pyc __pycache__/json*
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# Check for naming conflicts
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ls *.py | grep -E "^(json|os|sys|re|io)\.py$"
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```
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---
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## Key/Index Errors
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### KeyError
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```python
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KeyError: 'username'
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```
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**Causes**:
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1. Key doesn't exist in dict
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2. Typo in key name
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3. Data structure changed
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**Solutions**:
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```python
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# Use .get() with default
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username = data.get('username', 'anonymous')
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# Check before access
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if 'username' in data:
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username = data['username']
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# Use defaultdict
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from collections import defaultdict
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data = defaultdict(str)
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```
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---
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### IndexError: list index out of range
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```python
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IndexError: list index out of range
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```
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**Causes**:
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1. Accessing index beyond list length
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2. Empty list
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3. Off-by-one error
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**Solutions**:
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```python
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# Check length first
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if len(my_list) > index:
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value = my_list[index]
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# Use try/except
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try:
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value = my_list[index]
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except IndexError:
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value = default_value
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# Safe last element
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last = my_list[-1] if my_list else None
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```
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---
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## Value Errors
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### ValueError: invalid literal for int()
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```python
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ValueError: invalid literal for int() with base 10: 'abc'
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```
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**Causes**:
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1. Non-numeric string to int()
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2. Float string to int()
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3. Empty string
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**Solutions**:
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```python
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# Safe conversion
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def safe_int(value, default=0):
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try:
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return int(value)
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except (ValueError, TypeError):
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return default
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# Check first
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if value.isdigit():
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number = int(value)
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# For floats as strings
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number = int(float("3.14")) # -> 3
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```
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---
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### ValueError: too many values to unpack
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```python
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ValueError: too many values to unpack (expected 2)
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```
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**Causes**:
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1. Unpacking mismatch
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2. Data has more/fewer items than expected
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**Solutions**:
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```python
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# Use * to capture rest
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first, *rest = [1, 2, 3, 4] # first=1, rest=[2,3,4]
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first, second, *_ = [1, 2, 3, 4] # Ignore extras
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# Check length first
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if len(items) >= 2:
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a, b = items[0], items[1]
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```
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---
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## File Errors
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### FileNotFoundError
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```python
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FileNotFoundError: [Errno 2] No such file or directory: 'file.txt'
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```
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**Causes**:
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1. File doesn't exist
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2. Wrong path (relative vs absolute)
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3. Typo in filename
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**Solutions**:
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```python
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from pathlib import Path
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# Check existence
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path = Path('file.txt')
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if path.exists():
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content = path.read_text()
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# Use absolute path
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path = Path(__file__).parent / 'data' / 'file.txt'
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# Create if not exists
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path.parent.mkdir(parents=True, exist_ok=True)
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path.touch()
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```
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---
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### PermissionError
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```python
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PermissionError: [Errno 13] Permission denied: '/path/to/file'
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```
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**Causes**:
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1. No write permission
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2. File owned by another user
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3. File is read-only
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**Diagnosis**:
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```bash
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ls -la /path/to/file
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stat /path/to/file
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```
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**Solutions**:
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```bash
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# Change permissions
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chmod 644 /path/to/file
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chmod 755 /path/to/directory
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# Change ownership
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sudo chown $USER:$USER /path/to/file
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```
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```python
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# Write to user directory instead
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from pathlib import Path
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user_dir = Path.home() / '.myapp'
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user_dir.mkdir(exist_ok=True)
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```
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---
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## Encoding Errors
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### UnicodeDecodeError
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```python
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UnicodeDecodeError: 'utf-8' codec can't decode byte 0xff
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```
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**Causes**:
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1. File not UTF-8 encoded
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2. Binary file read as text
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3. Mixed encodings
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**Solutions**:
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```python
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# Try different encoding
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with open('file.txt', encoding='latin-1') as f:
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content = f.read()
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# Detect encoding
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import chardet
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with open('file.txt', 'rb') as f:
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result = chardet.detect(f.read())
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encoding = result['encoding']
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with open('file.txt', encoding=encoding) as f:
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content = f.read()
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# Ignore errors (lossy)
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with open('file.txt', encoding='utf-8', errors='ignore') as f:
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content = f.read()
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```
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---
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## JSON Errors
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### json.decoder.JSONDecodeError
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```python
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json.decoder.JSONDecodeError: Expecting value: line 1 column 1
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```
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**Causes**:
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1. Invalid JSON syntax
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2. Empty string/file
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3. HTML returned instead of JSON
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**Diagnosis**:
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```python
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# Print raw content first
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print(repr(response.text))
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print(response.text[:100])
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```
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**Solutions**:
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```python
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# Check before parsing
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if response.text:
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try:
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data = json.loads(response.text)
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except json.JSONDecodeError as e:
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print(f"Invalid JSON at line {e.lineno}, col {e.colno}")
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print(f"Content: {response.text[:200]}")
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# Handle HTML error pages
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if response.text.startswith('<'):
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raise ValueError("Received HTML instead of JSON")
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```
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---
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## Recursion Errors
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### RecursionError: maximum recursion depth exceeded
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```python
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RecursionError: maximum recursion depth exceeded
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```
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**Causes**:
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1. Infinite recursion
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2. Missing base case
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3. Deep data structure
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**Solutions**:
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```python
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# Increase limit (temporary fix)
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import sys
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sys.setrecursionlimit(10000)
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# Better: convert to iteration
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def factorial_iterative(n):
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result = 1
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for i in range(1, n + 1):
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result *= i
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return result
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# Use @lru_cache for memoization
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from functools import lru_cache
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@lru_cache(maxsize=None)
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def fib(n):
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if n < 2:
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return n
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return fib(n - 1) + fib(n - 2)
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```
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---
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## Async Errors
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### RuntimeError: Event loop is closed
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```python
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RuntimeError: Event loop is closed
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```
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**Causes**:
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1. Trying to use closed event loop
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2. Event loop not properly managed
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3. Windows-specific issue with ProactorEventLoop
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**Solutions**:
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```python
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# Use asyncio.run() (Python 3.7+)
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asyncio.run(main())
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# For Windows
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if sys.platform == 'win32':
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asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())
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# Explicit loop management
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loop = asyncio.new_event_loop()
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asyncio.set_event_loop(loop)
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try:
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loop.run_until_complete(main())
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finally:
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loop.close()
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```
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---
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### RuntimeError: cannot reuse already awaited coroutine
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```python
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RuntimeError: cannot reuse already awaited coroutine
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```
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**Causes**:
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1. Awaiting same coroutine twice
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2. Storing coroutine in variable and reusing
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**Solutions**:
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```python
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# Wrong - reusing coroutine
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coro = fetch_data()
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await coro
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await coro # Error!
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# Correct - create new coroutine each time
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await fetch_data()
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await fetch_data()
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# Or use asyncio.create_task for concurrent execution
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task1 = asyncio.create_task(fetch_data())
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task2 = asyncio.create_task(fetch_data())
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await asyncio.gather(task1, task2)
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```
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---
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## Quick Reference Table
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| Error | Category | Quick Fix |
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|-------|----------|-----------|
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| `ModuleNotFoundError` | Import | `pip install <pkg>` |
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| `ImportError: circular` | Import | Move import inside function |
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| `TypeError: NoneType subscript` | Type | Add `if x is not None` check |
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| `TypeError: not callable` | Type | Check for shadowed built-ins |
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| `AttributeError: NoneType` | Attribute | Guard against None |
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| `KeyError` | Dict | Use `.get()` with default |
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| `IndexError` | List | Check `len()` first |
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| `ValueError: int()` | Value | Use try/except |
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| `FileNotFoundError` | File | Use `Path.exists()` check |
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| `UnicodeDecodeError` | Encoding | Try `encoding='latin-1'` |
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| `JSONDecodeError` | JSON | Check response content first |
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| `RecursionError` | Recursion | Convert to iteration |
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Reference in New Issue
Block a user