Handling text with Python¶

Get started¶

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text1 = 'In this world nothing can be said to be certain except death and taxes'

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len(text1)

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text2 = text1.split(' ')

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len(text2)

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text2

1. Finding Specific Words¶

Words that are more than 5 letters long¶

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[w for w in text2 if len(w) > 5]

Words that end with 'd'¶

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[w for w in text2 if w.endswith('d')]

Words that start with 'd'¶

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[w for w in text2 if w.startswith('d')]

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[w for w in text2 if w.startswith(('d','n'))]

2. Using set()¶

Finding unique words from a list¶

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text3 = 'to be or not to be'
text4 = text3.split(' ')

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text4

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text5 = set(text4)

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len(text5)

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text5

set vs list performance¶

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import time
import random

NUMBER_OF_ELEMENTS = 10000

# Create a list
lst = list(range(NUMBER_OF_ELEMENTS))
random.shuffle(lst)

# Crt=eate a set from the list
s = set(lst)

# Test if an element is in the set
start = time.time()
for i in range(NUMBER_OF_ELEMENTS):
    i in s
end = time.time()
print(f'To test if {NUMBER_OF_ELEMENTS} elements are in the set, runtime is {end-start} seconds')

# Test if an element is in the list
start = time.time()
for i in range(NUMBER_OF_ELEMENTS):
    i in lst
end = time.time()
print(f'To test if {NUMBER_OF_ELEMENTS} elements are in the list, runtime is {end-start} seconds')

3. More String Operations¶

t in s - To check whether a substring exists in a given string¶

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'Python' in 'Python is good'

string.isupper() - To check whether all the characters of the string are uppercase¶

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'PYTHON IS GOOD'.isupper()

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'Python is good'.isupper()

string.islower() - To check whether all the characters of the string are lowercase¶

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'python is good'.islower()

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'Python is good'.islower()

string.istitle() - To check whether each word in the string starts with an uppercase letter¶

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'Python Is Good'.istitle()

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'Python is good'.istitle()

string.isdigit() - To check whether the string contains digits only¶

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'000002'.isdigit()

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'SZ000002'.isdigit()

string.isalpha() - To check whether the string contains alphabetic characters only¶

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'Textmining'.isalpha()

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'Text mining1'.isalpha()

string.isalnum() - To check whether the string contains alphanumeric characters only¶

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'SZ000002'.isalnum()

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'SZ_000002#'.isalnum()

Conversion between uppercase and lowercase¶

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s1 = 'python is good'

string.upper() - Returns a string in which all characters are uppercased¶

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s2 = s1.upper()

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s2

string.lower() - Returns a string in which all characters are lowercased¶

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s2.lower()

string.capitalize() - Returns a string with only its first character capitalized¶

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s1.capitalize()

string.title() - Returns a string in which first characters of all the words are capitalized¶

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s1.title()

string.split()¶

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s3 = 'cattcatt'
s4 = s3.split('a')

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s4

join()¶

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'a'.join(s4)

Get all the characters of s3¶

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list(s3)

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[c for c in s3]

String formatting¶

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'{} {}'.format('hello', 'world')

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'{} {}'.format(24, 'seconds')

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24 + 'seconds' 

f-string¶

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name = 'Eric'
age = 74

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f'Hello, {name}. You are {age}.'

string.strip() – Removes whitespaces at the beginning and at the end of the string¶

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s5 = '  a quick brown fox jumped over the lazy dog  '
s6 = s5.strip()

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s6

sring.replace(old, new) - Returns a string where all occurrences of the old substring are replaced with the new substring¶

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s6.replace('o', 'O')

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s6.replace('o', 'O', 2)

string.translate(table) - The translate() method returns a string where each character is mapped to its corresponding character in the translation table. The translation table is created by the static method maketrans().¶

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intab = 'aeiou'
outtab = '12345'
table = str.maketrans(intab, outtab)
s7 = 'aeiou-xmppp'

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s7.translate(table)

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table_1 = str.maketrans(intab, outtab, 'xm')

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s7.translate(table_1)

4. Index and Slice String¶

Accessing characters by positive index number¶

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s = 'Hello World!'

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s[4]

Accessing characters by negative index number¶

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s[-3]

Slicing strings¶

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s[1:5]

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s[:5]

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s[-4:-1]

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s[-2:]

Specifying stride while slicing strings¶

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s[:5]

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s[:5:1]

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s[:5:2]

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s[::-1]

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s[-1:-7:-2]

String.find() - Return the index of the first occurrence of the substring¶

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s.find('o')

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s.find('or')

5. Writing to and Reading from CSV File¶

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import csv

Writing to a csv file¶

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with open('test.csv', 'w', encoding='utf8', newline='') as wf:
    writer = csv.writer(wf)
    writer.writerow(('张三','北京'))

Reading from a csv file¶

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with open('test.csv', 'r', encoding='utf8') as rf:
    r = csv.reader(rf)
    for row in r:
        print(f'姓名:{row[0]}, 住址:{row[1]}')

Exercise1¶

Write a Python program to get a string from a given string where all occurrences of its first char have been changed to '@' except the first char itself.¶

Sample String : 'restart'¶

Expected Result : 'resta@t'¶

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def change_char(str1):
    ### START CODE HERE ###

    ### END CODE HERE ###
    return str1

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# Check your function
print(change_char('restart'))
print(change_char('text'))

Expected output¶

resta@t
tex@

Exercise2¶

Given an input string with the combination of the lower and upper case, arrange characters in such a way that all lowercase letters should come first.¶

Sample String : 'PyNaTive'¶

Expected Result : 'yaivePNT'¶

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def arrange_chars(str1):
   
  ### START CODE HERE ###

  ### END CODE HERE ###
  return str1

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# Check your function
print(arrange_chars('PyNaTive'))
print(arrange_chars('OpTYabi'))

Expected output¶

yaivePNT
pabiOTY

Exercise3¶

Write a Python function that takes a list of words and returns the word with the largest length.¶

Sample List : ["Python", "Text", "Analysis"]¶

Expected Result : 'Analysis'¶

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def find_longest_word(words_list):
    longest_word = ''
    max_len = 0
    ### START CODE HERE ###

    ### END CODE HERE ###
    return longest_word

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# Check your function
print(find_longest_word(["Python", "Text", "Analysis"]))

Expected output¶

Analysis

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