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python

**This is an old revision of the document!**

Table of Contents

Data Type
x = “Hello World” str
x = 20 int
x = 20.5 float
x = 1j complex
x = [“apple”, “banana”, “cherry”] list
x = (“apple”, “banana”, “cherry”) tuple
x = range(6) range
x = {“name” : “John”, “age” : 36} dict
x = {“apple”, “banana”, “cherry”} set
x = frozenset({“apple”, “banana”, “cherry”}) frozenset
x = True bool
x = b“Hello” bytes
x = bytearray(5) bytearray
x = memoryview(bytes(5))

ref: https://medium.com/@shawnren527/learn-about-python-3-data-types-numbers-and-strings-76c75a917c9b

Class

ref:https://www.w3schools.com/python/python_classes.asp

Create a list of objects from a class

snippet.python
   swatchList = []
   swatchList.append(Swatch("Sky1",22,40,76))
   # Swatch is the name of the class

Reference:
- A List of Class Objects

Format Variables

snippet.python
   print('%s %.2f' % ("hue =",swSky1.hue))
   print('{0} {1:.2f}'.format("hue =",swSky1.hue))
   print("hue =", format(swSky1.hue,'.2f'))
   # f:float, x:hex, s:string

The three lines above give the same result hue = 220.00.
The first line is the old way, “s” means string and “f” means float. The second line is the new way. 0 in {} refer to the first variable and 1:.2f in {} refers to the second variable swSky1.hue and format it to 2 digits behind decimal point.

Reference:
- Using % and .format() for great good!: https://pyformat.info/

Plot (matplotlib)

py37-matplotlib has the following notes:
The default backend is the interactive Mac OS X backend. Different backends can be specified using the ~/.matplotlib/matplotlibrc file. More details regarding backends can be found in the matplotlib FAQ: https://matplotlib.org/tutorials/introductory/usage.html#backends

snippet.python
import matplotlib.pyplot as plt
plt.plot(x, y, color='black', linestyle = 'none', marker='o', markerfacecolor=(swatch.r/255.0,swatch.g/255.0,swatch.b/255.0), markersize=12)

Note: markerfacecolor accept RGB, HEX and simple color text description: markerfacecolor=(r,g,b), markerfacecolor='#333399', markerfacecolor='green'

Common Error

snippet.python
    File "main.py", line 15
    self.sat = (cMax - cMin)/(1-abs(2*self.lum-1))
                                                 ^
    TabError: inconsistent use of tabs and spaces in indentation

Convert all tab to space will solve this problem.

python.1612188795.txt.gz · Last modified: 2021/02/01 22:13 by admin

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