Finished Chapter 10

.gitmodules

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+[submodule "pcc_2e"]
+	path = pcc_2e
+	url = git@github.com:ehmatthes/pcc_2e.git

chap10_file_exceptions.md

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+# Chapter 10. Files and Exceptions
+
+Files operation skipped here. Directly head to Exception
+
+## Exceptions
+
+* **exceptions** = objects python use to manage errors that arise during a program's execution. 
+* When python unsure what to do, exception object is created.
+  * If exceptions are handled correctly, program can continue run
+  * If don't handle exception, program will halt and show *traceback*
+
+Syntax of exception handling: `try-except`
+
+* `try` tells python do sth
+* `except` tell python what to do if an exception is raised.
+
+### e.g. ZeroDivisionError Exception
+
+* Simple error, python will create `ZeroDivisionError` in response to do "Divide by Zero".
+* When you think an error may occur, you can write a `try-except` block to handle exception
+
+```python
+try:
+    print(5/0)
+except ZeroDivisionError:
+    print("You can't divide by zero!")
+```
+
+If more code followed `try-except` block, the program would continue running. e.g. as shown below
+
+### Using Exceptions to Prevent Crashes
+
+Handling errors correctly is important when the program has more work to do after the error occurs.
+
+```python
+print("Give me two numbers, and I'll divide them.")
+print("Enter 'q' to quit.")
+
+while True:
+    first_number = input("\nFirst number: ")
+    if first_number == 'q':
+        break
+    second_number = input("Second number: ")
+    if second_number == 'q':
+        break
+    
+    answer = int(first_number) / int(second_number)
+    print(answer)
+```
+
+This function ask for numbers and will calculate division. To properly cover potential failure, use `try-except-else` block
+
+* `try` block: Python attempts to run code
+* `except` block: catch possible error
+* `else` block: if division operation is successful, carry on!
+
+Hence, program can be more robust
+
+```python
+    try:
+        answer = int(first_number) / int(second_number)
+    except ZeroDivisionError:
+        print("You can't divide by 0!")
+    else:
+        print(answer)
+```
+
+### Handling FileNotFoundError Exception
+
+```python
+filename = 'alice.txt'
+
+with open(filename, encoding='utf-8') as f:
+    contents = f.read()
+```
+
+If python cannot find `alice.txt`, it will raise halt, and show traceback
+
+```
+Traceback (most recent call last):
+  File "alice.py", line 6, in <module>
+    with open(filename, encoding='utf-8') as f:
+FileNotFoundError: [Errno 2] No such file or directory: 'alice.txt'
+```
+
+After changing python code to
+
+```python
+filename = 'alice.txt'
+
+try:
+    with open(filename, encoding='utf-8') as f:
+        contents = f.read()
+except FileNotFoundError:
+    print(f"Sorry, the file {filename} does not exist")
+```
+
+Python will show "Sorry, the file alice.txt does not exist"
+
+### Failing Silently
+
+If you want the program to fail silently and carry on, use `pass` to tell Python to do nothing, and skip the try-except-else blocks
+
+```python
+def count_words(filename):
+    """Count the approximate number of words in a file."""
+    try:
+        --snip--
+    except FileNotFoundError:
+        pass
+    else:
+        --snip--
+
+    filenames = ['alice.txt', 'siddhartha.txt', 'moby_dick.txt', 'little_women.txt']
+    for filename in filenames:
+        count_words(filename)
+```
+
+## Storing Data
+
+`json.dump()` & `json.load`

pcc

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+Subproject commit f555082df0f8268b8f269e59a99da8ed5013f749

pcc_2e

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+Subproject commit 078318e4c5a56959586a14dc03e988e9491d4cec

src/alice.py

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+filename = 'alice.txt'
+
+try:
+    with open(filename, encoding='utf-8') as f:
+        contents = f.read()
+except FileNotFoundError:
+    print(f"Sorry, the file {filename} does not exist")

src/divison_calculator.py

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+print("Give me two numbers, and I'll divide them.")
+print("Enter 'q' to quit.")
+
+while True:
+    first_number = input("\nFirst number: ")
+    if first_number == 'q':
+        break
+    second_number = input("Second number: ")
+    if second_number == 'q':
+        break
+    
+    try:
+        answer = int(first_number) / int(second_number)
+    except ZeroDivisionError:
+        print("You can't divide by 0!")
+    else:
+        print(answer)