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Commit 989081c

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added functions, tuples, error handling
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‎README.md‎

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@@ -145,6 +145,39 @@ Available in Python 3.6+. Works similar to the above, but is more powerful as ar
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'Five plus ten is 15 and not 30.'
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```
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## Function
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Function is a block of code which runs when it is called.
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Functions are declared using the `def` keyword. Function name must be a valid identifier.
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Function arguments can be literal values, variables (valid identifiers), and expressions.
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```python
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def sum(a, b) :
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return a + b
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def subtract(a, b) :
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return a - b
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def getPerson(name, age) :
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person = { "name": name, "age": age }
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return person
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```
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#### Function Call
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Functions can be called by passing the arguments according to the declaration.
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```python
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a = 20
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b = 50
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c = sum(a, b)
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d = sum(b, 50)
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e = subtract(b, a)
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p = getPerson("Joe", 25)
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# OUTPUT:
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print( "Sum - {} plus {}: {}" . format( a, b, c ) ) # Sum - 20 plus 50: 70
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print( "Sum - {} plus 50: {}" . format( b, d ) ) # Sum - 50 plus 50: 100
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print( "Subtraction - {} minus {}: {}" . format( b, a, e ) ) # Subtraction - 50 minus 20: 30
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print( "Person - {}" . format( p ) ) # Person - {'name': 'Joe', 'age': 75}
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```
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## Data Structures
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### Lists
@@ -186,8 +219,47 @@ len(<dict>) # Find the length of the diction
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```
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A dictionary can also contain many dictionaries, this is called nested dictionaries.
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## Third party libraries
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### Tuple
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A tuple is a collection which is ordered, indexed and unchangeable. In Python tuples are written with round brackets.
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```python
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this_tuple = ('books', 'pen', 'paper') # Defined a tuple
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# Accessing Tuple Items
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print(this_tuple[2]) # paper
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```
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#### Changing Tuple Values
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Tuples are immutable, which means they cant to changed once they are created.
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If a value inside tuple needs to be changed, the tuple must be converted to a list.
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Newly created list can be converted back to tuple after updating changes.
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```python
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desk_tuple = ("pen stand", "plant", "marker")
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desk_list = list(desk_tuple)
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desk_list[2] = "highlighter"
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desk_tuple = tuple(desk_list)
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print(desk_tuple[2]) # highlighter
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```
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#### Creating tuple with one item
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To create a tuple with only one item, you have to add a comma after the item, otherwise Python will not recognize it as a tuple.
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```python
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this_tuple = ("Python",)
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print(type(this_tuple)) # tuple
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# NOT a tuple
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this_tuple = ("Python")
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print(type(this_tuple)) # str
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```
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#### Deleting a tuple
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Tuples are unchangeable, so you cannot remove items from it, but you can delete the tuple completely:
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```python
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this_tuple = ('books', 'pen', 'paper')
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del this_tuple
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print(this_tuple) # ERROR: this_tuple is not defined
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## Third party libraries
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```
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### Pandas
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```shell
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$ sudo pip3 install pandas # Installing pandas module in Ubuntu
@@ -212,6 +284,59 @@ nltk.download('punkt')
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nltk.download('averaged_perceptron_tagger')
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```
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## Errors and Exceptions
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Program stops working on error Python raises exceptions when it encounter error.
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To avoid this, `try-catch` blocks are used.
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# Exceptions
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No syntax errors found, program starts execution.
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Errors detected during execution are called exceptions.
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Use try: except: finally: to catch and handle the exceptions.
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Use try: except: finally: to avoid program termination on exceptions.
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Use try: except: else: instead of try: except: finally: for alternate flows.
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Multiple except can be use to catch the exceptions.
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```python
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a = 10 * (1/0)
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# Throws division by zero exception and terminate the program
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# Traceback (most recent call last):
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File "", line 1, in
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a = 10 * (1/0)
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# ZeroDivisionError: division by zero
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# Updated Program - Valid - Try: Except: Finally
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b = 10
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try:
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a = 10 * (1/b)
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print( "a = {}" .format( a ) )
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except:
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print( "Caught divide by zero - while getting a" )
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print( "Execute on error - b must be non-zero value" )
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finally:
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print( "Execute Always - normal and exceptional flow" )
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# OUTPUT
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a = 1.0
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Execute Always - normal and exceptional flow
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## Updated Program - Error - Try: Except: Finally
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b = 0
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try:
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a = 10 * (1/b)
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print( "a = {}" .format( a ) )
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except:
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print( "Caught divide by zero - while getting a" )
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print( "Execute on error - b must be non-zero value" )
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else:
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print( "Alternate to exceptional flow" )
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# Output
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Caught divide by zero - while getting a
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Execute on error - b must be non-zero value
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Execute Always - normal and exceptional flow
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```
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## Python Snippets
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### Anagrams
@@ -262,4 +387,4 @@ def write_to_file(filename, content):
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except Exception as e:
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print("Failed to write to file with error: ")
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print(e)
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```
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```

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