In our previous lesson we discussed about Variables, basic data types and operators. If you haven't gone through it read it here.
A string is traditionally a sequence of characters. Strings are one of the common data types in all programming languages and python is not an exception.
String in Python is handled with str object and strings are immutable sequences.
Strings can be represented in various of ways in Python:
# Using Single Quotes
my_string1 = 'This is a string'
# Using Double Quotes
my_string2 = "This is a string too".
# Using Triple Quotes (Multiline strings)
my_string3 = '''Lorem ipsum dolor sit amet, consectetur adipiscing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. '''
# You could write it with double quotes as well
my_string3 = """Lorem ipsum dolor sit amet, consectetur adipiscing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. """The operations in the following table are supported by most sequence types, both mutable and immutable. Since strings are also sequences they support them all.
| Operation | Result |
|---|---|
| x in s | True if an item of s is equal to x, else False |
| x not in s | False if an item of s is equal to x, else True |
| s + t | the concatenation of s and t |
| s * n or n * s | equivalent to adding s to itself n times |
| s[i] | ith item of s, origin 0 |
| s[i:j] | slice of s from i to j |
| s[i:j:k] | slice of s from i to j with step k |
| len(s) | length of s |
| min(s) | smallest item of s |
| max(s) | largest item of s |
| s.index(x[, i[, j]]) | index of the first occurrence of x in s (at or after index i and before index j) |
| s.count(x) | total number of occurrences of x in s |
Check the official about these operations here.
Following are some of the common string methods supported by str objects.
| Method | Description |
|---|---|
| capitalize() | Return a new string with its first character capitalized and the rest lowercased. |
| endswith(suffix[, start[, end]) | Check if the string ends with the given suffix. Return boolean result True or False |
| startswith(prefix[, start[, end]]) | Check if the string starts with the given prefix and return boolean result True or False |
| find(sub[, start[, end]]) | Return the first index in the string where substring sub is found within start to end of the string. Return -1 if not found. |
| strip([chars]) | Return a new string with the leading and trailing characters removed. The optional chars argument defaults to removing whitespace. |
| swapcase() | Return a new string with uppercase characters converted to lowercase and vice versa. |
| title() | Return a new titlecased version of the string where words start with an uppercase character and other letters are lowercased. |
| upper() | Return a new uppercased version of the string. |
| lower() | Return a new lowercased version of the string. |
| split(sep=None, maxsplit=-1) | Splits the string into substring using the sep argument as the separator. Return the list of splitted substrings. |
| format(*args, **kwargs) | Perform a string formatting operation and return the formatted string. |
| replace(old, new[, count]) | Return a new string by replacing all occurrences of substring old with new. If count argument is provided, only count number of replacements would be done. |
The above listed methods are just some handful of common string methods. Check the official docs for the full list.
text = input('Enter a string: ')
print("capitalize() = ", text.capitalize())
print("strip() = ", text.strip())
print("swapcase() = ", text.swapcase())
print("title() = ", text.title())
print("upper() = ", text.upper())
print("lower() = ", text.lower())
print("replace('a', 'b') = ", text.replace('a', 'b'))
print("endswith('foo') = ", text.endswith('foo'))
print("startswith('bar') = ", text.startswith('bar'))
print("find('foo') = ", text.find('foo'))
print("split(' ') = ", text.split(' '))You probably remember the printf function if you've programmed in C. You can do similar string formatting in Python as well.
You would do something like this.
print("Hello %s!" % name)# Ask the user to enter first and last name.
first_name = input('Your first name: ')
last_name = input('Your last name: ')
print("\nHi %s %s!" % (first_name, last_name))
print("It's nice to meet you.")# Ask the user to enter first and last name.
PI = 3.1415
radius = input('Enter radius of circle(meters): ')
area = PI * float(radius) ** 2
print("\nArea of circle = %.2f sq. metres" % area)Following are the supported conversion types.
| Conversion | Meaning |
|---|---|
| 'd' | Signed integer decimal. |
| 'i' | Signed integer decimal. |
| 'o' | Signed octal value. |
| 'u' | Obsolete type – it is identical to 'd'. |
| 'x' | Signed hexadecimal (lowercase). |
| 'X' | Signed hexadecimal (uppercase). |
| 'e' | Floating point exponential format (lowercase). |
| 'E' | Floating point exponential format (uppercase). |
| 'f' | Floating point decimal format. |
| 'F' | Floating point decimal format. |
| 'g' | Floating point format. Uses lowercase exponential format if exponent is less than -4 or not less than precision, decimal format otherwise. |
| 'G' | Floating point format. Uses uppercase exponential format if exponent is less than -4 or not less than precision, decimal format otherwise. |
| 'c' | Single character (accepts integer or single character string). |
| 'r' | String (converts any Python object using repr()). |
| 's' | String (converts any Python object using str()). |
| 'a' | String (converts any Python object using ascii()). |
| '%' | No argument is converted, results in a '%' character in the result. |
For in-depth information about the C-style formatting check the official docs.
The C-Style formatting is already powerful. But python provides another way for formatting as well.
That is using str.format() method.
Something like this:
print("Hello {}!".format(name))Pretty much the same, right?
Okay, check this example on what difference this new syntax makes.
first_name = input('Your first name: ')
last_name = input('Your last name: ')
# Old style formatting.
print('Hello %s %s!' % (first_name, last_name))
# New Style formatting
print('Hello {} {}!'.format(first_name, last_name))
print('Hello {0} {1}!'.format(first_name, last_name))
# This is where, you will feel the difference.
print('Hello {1} {0}!'.format(first_name, last_name))
print('Hello {0} {0} {1}!'.format(first_name, last_name))amount = input('Enter amount in USD: ')
rate = 100.00
amount_npr = float(amount) * rate
print('Equivalent amount: NPR. {:.2f}'.format(amount_npr))-
Write a program to ask for the marks of 5 different subjects and print the total marks obtained and the total percentage.
-
Write a program to ask for the equation of a line in the form
y = mx + c. And print the values of slope and y-intercept of the line. (Hint: Usesplit().) -
Write a program to ask for the user's date of birth in
YYYY-MM-DDformat and calculate the user's age. (Hint: Usesplit()method to split the date parts.)
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