01 PDT - 05 String Manipulation

The str datatype represents a string, which is a sequence of characters. Strings in Python are enclosed in single quotes ('), double quotes ("), or triple quotes (''' or """) for multi-line strings.

• A single character is treated the same as a string of length 1.
• Strings are immutable: once created, they cannot be changed.

String Representation

• Anything inside single (') or double quotes (") is a string.

string1 = "Hello, World!"
string2 = 'Python is awesome'

You can use one type of quote inside the other without escaping:

string3 = "He said, 'Hello!'"
string4 = 'She replied, "Good morning!"'

For multi-line strings, use triple quotes:

multiline_string = '''This is a string
that spans multiple lines.'''
print(multiline_string)

Avoiding Syntax Errors with Strings

To avoid errors when using quotes within strings, you can:

• Use different quote types inside and outside:

print("Hello, 'friend'")  # Using double quotes for the string
print('Hello, "friend"')  # Using single quotes for the string

• Escape quotes with a backslash (\):

print("Hello, \"friend\"")  # Escape double quotes
print('Hitchhiker\'s Guide to the Galaxy')  # Escape single quote

f-strings (Formatted Strings)

An f-string (formatted string) allows embedding expressions inside string literals for formatting. To use an f-string, prefix the string with an f and include expressions inside curly braces ({}).

name = input("What's your name? ")
print(f"Hello, {name}!")  # Inserts the value of 'name' inside the string

first = "John"
last = "Doe"
print(f"Hello, {first} {last}!")  # Output: Hello, John Doe!

name = "john"
print(f"Hello, {name.title()}!")  # Output: Hello, John!

Basic String manipulation

Combining two strings / Concatenation “+”

“+” concatenates the two strings like a text, its just one argument

name = input ("wht is ")         
print("hello "+ name)

s = "hello"
t = s + ", there"

" , " creates two arguments. The default parameters of print function adds a space between arguments.

print("hello", name)

sep=' ' is the space between the arguments and end="\n" is a new line at the end.

print("hello", name, sep="", end="\n\n\n")

This has no space and 3 extra lines.

Adding White Space

White space refers to non printing characters. Adding white space to strings with tabs or newlines \t to add tab to the text. \n to add a new line in a string

print( "\tpython")

    python

\n \t tells python to move to new line and start with tab space.

print( "Languages:\nPython\nJava\nJava Sricpt"  )

Python

Java

Java Sricpt

print("Continue on the", end = " " )   # no new line
print("same line", end= ".\n")   
print("Next line.")

Continue on the same line.
Next line.

Getting to individual characters

str is a sequence or list of characters. Positions are 0, 1, 2, . .n-1  for string of length n. -5, -4, -3, -2, -1  to count backwards.

S = "hello"
S[1] = "e"
S[-1] = "o"
S[-2] = "l"

s = "hello"
t = "there"
s+t = "hellothere"

len(s)  # returns length of s

Extracting Sub-strings and Slices

Slice is a segment of a string.

s = "hello"
s[1:4] # is "ell" as slice stops before the last number
s[:j]  # starts from 0 and ends at j-1
s[i:]  # i onwards till the end

Modifying strings

Strings are Immutable values, We cannot update a string in place.
They cannot be changed directly without creating another value.

s = "hello" # to change it to "help"
s[3] = "p"  # will cause error

# instead, use slices and cocatination
s = "hello"
s = s[0:3] + "p!"
s = "help!"

Removing a letter from index and adding to new string

Using += (reverse of =+ as in int)

merged = ""
word1 = "abcdef"
merged += word1[0]
merged += word1[1]

# merged = "ab"

Making a list of individual strings from a string

word1 = "abcdef"
ind = list(word1)
print(ind)   # ['a', 'b', 'c', 'd', 'e', 'f']

Joining a list of strings

Recombining a list of strings using a separator

seperator.join(list of strings)

columns = ['6', '7', '8']  # has list of strings 
joiningstring = ","   # this will be the seperator
csline = joiningstring.join(columns)  #  ",".join(columns)

date = "16"
month = "08"
year = "2016"

# the seperator can be directly given as in "_"
today = "_".join( [date, month, year])  

Using of set to have unique entries

Set creates a list of only unique characters, no repeats.

word1 = "abababab"
ind = set(word1)
print(ind)
# {'b', 'a'}   returns a dict?
# set doesnt provide indexing!! or any order 

# make a list and pass or pass str directly, gives same result