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- #!/usr/bin/env python
- # coding: utf-8
- # # Names
- #
- # Names are given to values in Python using an *assignment* statement. In an assignment, a name is followed by `=`, which is followed by any expression. The value of the expression to the right of `=` is *assigned* to the name. Once a name has a value assigned to it, the value will be substituted for that name in future expressions.
- # In[1]:
- a = 10
- b = 20
- a + b
- # A previously assigned name can be used in the expression to the right of `=`.
- # In[2]:
- quarter = 1/4
- half = 2 * quarter
- half
- # However, only the current value of an expression is assigned to a name. If that value changes later, names that were defined in terms of that value will not change automatically.
- # In[3]:
- quarter = 4
- half
- # Names must start with a letter, but can contain both letters and numbers. A name cannot contain a space; instead, it is common to use an underscore character `_` to replace each space. Names are only as useful as you make them; it's up to the programmer to choose names that are easy to interpret. Typically, more meaningful names can be invented than `a` and `b`. For example, to describe the sales tax on a $5 purchase in Berkeley, CA, the following names clarify the meaning of the various quantities involved.
- # In[4]:
- purchase_price = 5
- state_tax_rate = 0.075
- county_tax_rate = 0.02
- city_tax_rate = 0
- sales_tax_rate = state_tax_rate + county_tax_rate + city_tax_rate
- sales_tax = purchase_price * sales_tax_rate
- sales_tax
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