Tokenization basics in Data Analysis Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is tokenization in text data processing?

Tokenization is the process of breaking down text into smaller pieces called tokens, such as words or sentences, to make it easier to analyze.

beginner

Why do we tokenize text before analysis?

We tokenize text to convert it into manageable parts so computers can understand and analyze the text more easily, like counting words or finding patterns.

beginner

Which Python library is commonly used for tokenization?

The NLTK (Natural Language Toolkit) library is commonly used for tokenization in Python.

beginner

What is the difference between word tokenization and sentence tokenization?

Word tokenization splits text into individual words, while sentence tokenization splits text into sentences.

beginner

Show a simple Python example to tokenize a sentence into words using NLTK.

from nltk.tokenize import word_tokenize
text = "Hello, how are you?"
tokens = word_tokenize(text)
print(tokens)

This code splits the sentence into words like ['Hello', ',', 'how', 'are', 'you', '?'].

What does tokenization do in text processing?

A Breaks text into smaller pieces called tokens

B Converts text to numbers directly

C Removes all punctuation from text

D Translates text to another language

Tokenization breaks text into smaller parts like words or sentences to help analyze it.

Which of these is a token in tokenization?

A A whole paragraph

B A word

C A book

D A language

Tokens are small pieces like words or sentences, not large blocks like paragraphs or books.

Which Python library is popular for tokenization?

A NLTK

B Pandas

C NumPy

D Matplotlib

NLTK is a popular library for natural language processing tasks including tokenization.

What is the output of word tokenization on the sentence 'Hi there!'?

A ['Hi there!']

B ['H', 'i', 't', 'h', 'e', 'r', 'e']

C ['Hi there']

D ['Hi', 'there', '!']

Word tokenization splits the sentence into words and punctuation marks as separate tokens.

Sentence tokenization splits text into:

A Words

B Paragraphs

C Sentences

D Characters

Sentence tokenization breaks text into sentences.

Explain what tokenization is and why it is important in text analysis.

Think about how computers understand text.

Describe the difference between word tokenization and sentence tokenization with examples.

Consider how you read a paragraph.

Practice

1. What is the main purpose of tokenization in text analysis?

easy

A. To split text into smaller parts called tokens

B. To translate text into another language

C. To remove all punctuation from text

D. To count the number of characters in text

Solution

1. Step 1: Understand tokenization concept

   Tokenization means breaking text into smaller pieces called tokens, like words or sentences.

2. Step 2: Compare options with definition

   Only To split text into smaller parts called tokens correctly describes tokenization as splitting text into tokens.

3. Final Answer:

   To split text into smaller parts called tokens -> Option A

4. Quick Check:

   Tokenization = splitting text [OK]

Hint: Tokenization means splitting text into pieces [OK]

Common Mistakes:

• Confusing tokenization with translation
• Thinking tokenization removes punctuation only
• Mixing tokenization with counting characters

2. Which of the following is the correct way to import the word_tokenize function from nltk in Python?

easy

A. from nltk import word_tokenize.tokenize

B. import nltk.word_tokenize

C. from nltk.tokenize import word_tokenize

D. import word_tokenize from nltk.tokenize

Solution

1. Step 1: Recall correct Python import syntax

   The correct syntax to import a function from a module is 'from module import function'.

2. Step 2: Match syntax with nltk tokenization import

   from nltk.tokenize import word_tokenize matches this syntax exactly for word_tokenize from nltk.tokenize.

3. Final Answer:

   from nltk.tokenize import word_tokenize -> Option C

4. Quick Check:

   Correct import syntax = from nltk.tokenize import word_tokenize [OK]

Hint: Use 'from module import function' to import specific functions [OK]

Common Mistakes:

• Using dot notation incorrectly in import
• Trying to import with 'import function from module'
• Confusing module and function names

3. What will be the output of the following code?

from nltk.tokenize import word_tokenize
text = "Hello, world! Let's tokenize this sentence."
tokens = word_tokenize(text)
print(tokens)

medium

A. ['Hello', ',', 'world', '!', 'Let', "'s", 'tokenize', 'this', 'sentence', '.']

B. ['Hello world Lets tokenize this sentence']

C. ['Hello', 'world', 'Lets', 'tokenize', 'this', 'sentence']

D. ['Hello,', 'world!', "Let's", 'tokenize', 'this', 'sentence.']

Solution

1. Step 1: Understand nltk.word_tokenize behavior

   word_tokenize splits text into words and punctuation as separate tokens, including contractions.

2. Step 2: Analyze the given text tokenization

   It splits "Hello," into 'Hello' and ',', "world!" into 'world' and '!', and "Let's" into 'Let' and "'s" separately.

3. Final Answer:

   ['Hello', ',', 'world', '!', 'Let', "'s", 'tokenize', 'this', 'sentence', '.'] -> Option A

4. Quick Check:

   word_tokenize splits punctuation and contractions separately [OK]

Hint: word_tokenize splits punctuation and contractions separately [OK]

Common Mistakes:

• Assuming punctuation stays attached to words
• Ignoring splitting of contractions
• Expecting a single string token

4. Identify the error in this tokenization code snippet:

import nltk
text = "Data Science is fun!"
tokens = nltk.word_tokenize(text)
print(tokens)

medium

A. word_tokenize is not a function in nltk

B. Missing import of word_tokenize from nltk.tokenize

C. text variable is not defined

D. print statement syntax error

Solution

1. Step 1: Check how word_tokenize is accessed

   word_tokenize is inside nltk.tokenize module, not directly under nltk.

2. Step 2: Identify import mistake

   Importing only nltk does not allow calling nltk.word_tokenize; must import from nltk.tokenize.

3. Final Answer:

   Missing import of word_tokenize from nltk.tokenize -> Option B

4. Quick Check:

   word_tokenize needs correct import [OK]

Hint: Import word_tokenize from nltk.tokenize, not just nltk [OK]

Common Mistakes:

• Calling nltk.word_tokenize without proper import
• Assuming all functions are directly under nltk
• Ignoring module structure

5. You have a list of sentences and want to tokenize each sentence into words, then count total tokens. Which code correctly does this using nltk's word_tokenize?

hard

A. from nltk.tokenize import word_tokenize
sentences = ["I love data.", "Tokenization is key."]
tokens = word_tokenize(sentences)
print(len(tokens))

B. import nltk
sentences = ["I love data.", "Tokenization is key."]
tokens = nltk.word_tokenize(sentences)
print(len(tokens))

C. from nltk.tokenize import word_tokenize
sentences = "I love data. Tokenization is key."
tokens = word_tokenize(sentences)
print(tokens)

D. from nltk.tokenize import word_tokenize
sentences = ["I love data.", "Tokenization is key."]
tokens = [word_tokenize(s) for s in sentences]
total = sum(len(t) for t in tokens)
print(total)

Solution

1. Step 1: Understand input and function usage

   word_tokenize expects a string, so to tokenize multiple sentences, tokenize each string separately.

2. Step 2: Analyze each option's approach

   from nltk.tokenize import word_tokenize sentences = ["I love data.", "Tokenization is key."] tokens = [word_tokenize(s) for s in sentences] total = sum(len(t) for t in tokens) print(total) tokenizes each sentence in a list comprehension, then sums lengths correctly. Some options wrongly pass list to word_tokenize. from nltk.tokenize import word_tokenize sentences = "I love data. Tokenization is key." tokens = word_tokenize(sentences) print(tokens) tokenizes a single string, not list.

3. Final Answer:

   The correct code tokenizes each sentence and counts total tokens -> Option D

4. Quick Check:

   Tokenize each sentence separately, then count tokens [OK]

Hint: Tokenize each sentence string separately, then count tokens [OK]

Common Mistakes:

• Passing list directly to word_tokenize
• Not summing token counts correctly
• Tokenizing entire text as one string when list given