Python Data Science Toolbox Part 1 Learning 1

User-defined functions

from:https://campus.datacamp.com/courses/python-data-science-toolbox-part-1/writing-your-own-functions?ex=1

• Strings in Python

 To assign the string

company = 'DataCamp'

You've also learned to use the operations + and * with strings. Unlike with numeric types such as ints and floats, the + operator concatenates strings together, while the * concatenates multiple copies of a string together. In this exercise, you will use the + and * operations on strings to answer the question below. Execute the following code in the shell:

object1 = "data" + "analysis" + "visualization"
object2 = 1 * 3
object3 = "1" * 3

->object1 contains "dataanalysisvisualization", object2contains 3, object3 contains "111".

• Recapping built-in functions

• Assign str(x) to a variable y1: y1 = str(x)
• Assign print(x) to a variable y2: y2 = print(x)
• Check the types of the variables x, y1, and y2.

->x is a float, y1 is a str, and y2 is a NoneType.

 It is important to remember that assigning a variable y2 to a function that prints a value but does not return a value will results in that variable y2 being oftype NoneType.

• Write a simple function

 You can use it as a pattern to define shout().

def square():
    new_value = 4 ** 2
    return new_value

# Define the function shout
def shout():
"""Print a string with three exclamation marks"""
# Concatenate the strings: shout_word
shout_word = 'congratulations'+ '!!!'

# Print shout_word
print(shout_word)

# Call shout
shout()

• Single-parameter functions

You will now update shout() by adding a parameter so that it can accept and process any string argument passed to it.

# Define shout with the parameter, word
def shout(word):
"""Print a string with three exclamation marks"""
# Concatenate the strings: shout_word
shout_word = str(word) + '!!!'

# Print shout_word
print(shout_word)

# Call shout with the string 'congratulations'
shout('congratulations')

• Functions that return single values

You're getting very good at this! Try your hand at another modification to the shout() function so that it now returns a single value instead of printing within the function. Recall that thereturn keyword lets you return values from functions.

# Define shout with the parameter, word
def shout(word):
"""Return a string with three exclamation marks"""
# Concatenate the strings: shout_word
shout_word = str(word) + '!!!'

# Replace print with return
return shout_word

# Pass 'congratulations' to shout: yell
yell = shout('congratulations')

# Print yell
print(yell)

Multiple parameters and return values

• Functions with multiple parameters

Here, you will modify shout() to accept two arguments. 

# Define shout with parameters word1 and word2
def shout(word1,word2):
"""Concatenate strings with three exclamation marks"""
# Concatenate word1 with '!!!': shout1
shout1 = word1 + '!!!'

# Concatenate word2 with '!!!': shout2
shout2 = word2 + '!!!'

# Concatenate shout1 with shout2: new_shout
new_shout = shout1 + shout2

# Return new_shout
return new_shout

# Pass 'congratulations' and 'you' to shout(): yell
yell = shout('congratulations', 'you')

# Print yell
print(yell)

• A brief introduction to tuples

how to construct, unpack, and access tuple elements. 

a, b, c = even_nums

# Unpack nums into num1, num2, and num3
print(nums)
num1, num2, num3 = (3, 4, 6)

# Construct even_nums
print(nums)
nums = (2, 4, 6)
print(nums)
even_nums = nums
print(even_nums)

• Function that return multiple values

 Here you will return multiple values from a function using tuples.

Note that the return statement return x, y has the same result as return (x, y): the former actually packs x and yinto a tuple under the hood!

# Define shout_all with parameters word1 and word2
def shout_all(word1, word2):

# Concatenate word1 with '!!!': shout1
shout1 = word1 + '!!!'

# Concatenate word2 with '!!!': shout2
shout2 = word2 + '!!!'

# Construct a tuple with shout1 and shout2: shout_words
shout_words = (shout1, shout2)

# Return shout_words
return shout_words

# Pass 'congratulations' and 'you' to shout_all(): yell1, yell2
yell1, yell2 = shout_all('congratulations','you')

# Print yell1 and yell2
print(yell1)
print(yell2)

Bringing it all together

• Bringing it all together (1)

You've learned how to add parameters to your own function definitions, return a value or multiple values with tuples, and how to call the functions you've defined.

For this exercise, your goal is to recall how to load a dataset into a DataFrame. The dataset contains Twitter data and you will iterate over entries in a column to build a dictionary in which the keys are the names of languages and the values are the number of tweets in the given language. The file tweets.csv is available in your current directory.

# Import pandas
import pandas as pd

# Import Twitter data as DataFrame: df
df = pd.read_csv('tweets.csv')

# Initialize an empty dictionary: langs_count
langs_count = {}

# Extract column from DataFrame: col
col = df['lang']

# Iterate over lang column in DataFrame
for entry in col:

# If the language is in langs_count, add 1
if entry in langs_count.keys():
langs_count[entry] += 1
# Else add the language to langs_count, set the value to 1
else:
langs_count[entry] = 1

# Print the populated dictionary
print(langs_count)

Great job! You've now defined the functionality for iterating over entries in a column and building a dictionary with keys the names of languages and values the number of tweets in the given language.

• Bringing it all together (2)

In this exercise, you will define a function with the functionality you developed in the previous exercise, return the resulting dictionary from within the function, and call the function with the appropriate arguments

For your convenience, the pandas package has been imported aspd and the 'tweets.csv' file has been imported into thetweets_df variable.

# Define count_entries()
def count_entries(df, col_name):
"""Return a dictionary with counts of
occurrences as value for each key."""

# Initialize an empty dictionary: langs_count
langs_count = {}

# Extract column from DataFrame: col
col = df[col_name]

# Iterate over lang column in DataFrame
for entry in col:

# If the language is in langs_count, add 1
if entry in langs_count.keys():
langs_count[entry] += 1
# Else add the language to langs_count, set the value to 1
else:
langs_count[entry] = 1

# Return the langs_count dictionary
return langs_count

# Call count_entries(): result
result = count_entries(tweets_df,'lang')

# Print the result
print(result)