Python Part2: Conditional statements, While loops, Strings and Range

Conditional statements

If expr:
     print("expr is true")

If expr:
     print("It's true")
else:
     print("its’s false")


Python provides the elif keyword to eliminate the need for nested if … else structure.

h = 5
if h > 5:
      print("greater than 5")
elif h < 2:
      print("less than 2")
else:
      print("between 2 and 5.")


While loops

# While loop 
 While expr: 
     print("loop while expr is true") 

# Do-while in python 
 While True: 
     If expr: 
          Break

Strings

• Immutable sequence of Unicode codepoints.
• Immutable mean when you construct a string you can't modify its content.
• Strings with Newlines
• Multiline strings
• """ this is
• Multiline string"""
• Escape sequences
• This is \nmultiline \nstring.
• len(s) gives number of codepoints(characters).
• The + operator can be used for string concatenation.
• >>> "This" + "is" + "a" + "string"
• Thisisastring
• Strings are immutable, so the += operator re-binds the reference to a new object. 
• Use sparingly, concatenation with + or += can cause performance degradation. 
• Call the join() method on the separator string. 
• >>> Numbers = ';'.join([1, 2, 3, 4]) 
• '1;2;3;4' 
• Use the split() to divide a string into a list. 
• >>> Numbers.split(';') 
• [1, 2, 3, 4] 
• Without an argument, split() divides on whitespace.
• Join()-ing on an empty separator is an important and fast way of concatenating a collection of strings. 
• The partition() method divides a string into three around a separator: prefix, separator, suffix.
• Tuple unpacking is useful to destructure the result.

Range

• Arithmetic progression of integers. 
• Stop value is one-past-the-end. 
• >>> range(5) 
• range(0, 5) 
• Ranges are 'half open'-start is include but stop is not. 
• >>> for I in range(5) 
• print(I) 
• 0 
• 1 
• 2 
• 3 
• 4
• Stop value of a range used as start value of consecutive range. 
• >>> list(range(5, 10)) 
• [5, 6, 7, 8, 9] 
• >>> list(range(10, 15)) 
• [10, 11, 12, 13, 14] 
• Optional third step value. 
• >>> List(range(0, 10, 2)) 
• [0, 2, 4, 6, 8] 
• Range(stop) range(10) 
• Range(start:stop) range(0, 10) 
• Range(start:stop:step) range(0, 10, 2)

See Also