Programming

  minte9
LearnRemember



Strings / Slice 

A slice is a segment of string
Strings are immutable

str[0:2]

Slice

A segment of string is called slice. 
 
# Slice a segment from a string

str = "banana"

print(str[0:2]) # ba
print(str[:2]) # ba
print(str[2:]) # nana

Immutable

Strings are immutable, you can't change them. 
 
# You can't change a string ...
# it is imutable

str = "Hello World"
str[0] = "J"
    # TypeError: 'str' object does not support item assignment

Key

To search in a string, use a loop through string. 
 
# Find key in a string

def find_key(str, ch):
    i = 0
    while i < len(str):
        if str[i] == ch:
            return i
        i = i + 1
    return -1

print(find_key("Hello World", "o"))  # 4

File

Open words.txt and search through words list. 
 
# Open file and search through words list
# Return number of words with no e in them

import os

file = os.path.dirname(__file__) + "/words.txt"
rows = open(file)

def has_no_e(word):
    for letter in word:
        if letter == "e":
            return False
    return True

W = [] # words
E = [] # word with no e

for row in rows:
    word = row.strip()
    W.append(word)
    if (has_no_e(word)):
        E.append(word)  
    

print("W: " + repr(len(W)))
print("E: " + repr(len(E)))

Build-in

Strings provide methods for various operations. 
 
# String built-in methods

str = "Hello World"

str = str.upper()
print(str)
    # HELLO WORLD

index = str.find("W")
print(index)
    # 6




References