Python tutorials

Installation

  • Anaconda: a comprehensive Python distribution with conda package manager and an array of scientific python packages

Writing and running

Plain Python files *.py

Jupyter notebooks *.ipynb

  • Jupyterlab/ Jupiter notebook (included in Anaconda dist.)

  • VS Code

Tutorial and reference

Variable and data types

  • Assignment (=) : binding a label to an object (data) so you could use it later.

  • Data includes boolean (True/False), numbers (integers, floating-point numbers), text strings, and more.

x = 1
type(x)
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# String, this is a comment and the Python intepreter will ignore it
greet= "Hello"  # The same as greet= 'Hello'
type(greet)
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# print function
print(greet, "world", x)
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Hello world 1 
# Floats
y = 1.0
type(y)
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# Boolean
type(True)
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# Scientific notation
z = 1e-3
z
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Python as a (fancy) calculator

# + - * / ** % //
# ----------------------------
x = 4
y = 3.0
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x + y
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x - y
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x * y
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x / y
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x // y
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x ** y
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x % y
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a = 10
a = a + 1
a
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a = 10
a *= 2
a
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# Multiple assignments
a, b = 11, 12
print(a, b)
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11 12 
# swap
b, a = a, b
print(a, b)
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12 11

String operations

# Repeating string
repetition = 10
'abc' * repetition
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# Concat strings
'a' + 'b'
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# f-string to insert values to a string (Python 3.6+)
numofcats = 10
f"I have {numofcats} cat(s)."
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x, y = "CAPITAL", 'smol'
x.lower(), y.upper()
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'gmail.com'.find('.com')
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string = 'qwqwqwqwqw'
string[2:5:2]
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join()

toJoin = ['This', 'is', 'a', 'string']
# ' '.join(toJoin)
' + '.join(toJoin)
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Containers

  • List

  • Tuple

  • Dictionary

  • (Set)

List

# lis = []
# lis = list((2, 3, 4))
# lis
lis = [0, 1, 2, 3]
# lis.append(4)
lis.extend(lis)
lis.insert(0, -1)
lis
lis.remove(1)
lis
lis.count(0)
lis
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lis = [[1, 1, 1], [2, 2, 2]]
lis[0][0]
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lis = [0, 1, 2, 3, 2, 3, 5]
# print(sorted(lis))
# print(lis)
# print(lis)
# lis.sort(reverse=True)
# lis.reverse()
# lis
# print(lis)
# a = reversed(lis)
for i in lis:
    print(i)
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0 1 2 3 2 3 5

Tuple

# tuple list str dict set...
# (a, b) = (2, 3)
# a
# a = (2, 3)
# a
# a[1]
# a = ('one', 'two')
# a
# a = (2, 3, 4, 5)
# a
# print(a, len(a))
# a = tuple([1, 1])
# a
# a[1] = 4
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lis = [4, 2, 1, 7, 9, 10]
# print(sorted(lis).index(1))
# for i in range(len(lis)):
#     print(i, lis[i])
# for i, v in enumerate(lis):
#     print(i, v)
# 4 in lis
# for i in range(10):
#     if (i in lis):
#         print('Found', i)
# lis[2:]
# lis[:2]
# lis[1:4:2]
lis = []
for i in range(10):
    lis.append(2 * i)
lis
lis = [i for i in range(1, 10) if i % 2 == 0]
lis
# lis = [i ** 2 for i in lis]
# lis
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lis1 = [2, 3, 4]
# sum(lis1)
min(lis1)
# max(lis1)
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# shallow copy
lis1 = [2, 3, 4]
lis2 = lis1
lis1.append(5)
lis2
# lis1 == lis2
# lis1 is lis2
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# deep copy
import copy
lis1 = [2, 3, 4]
lis2 = copy.deepcopy(lis1)
# lis1.append(5)
lis2
# lis1 == lis2
lis1 is lis2
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Dictionary

d = dict()
d = {}
# d[1] = 'one'
# d
# d[2] = 'two'
# d
d = {'one': 1, 'two': 2}
d
d.update({'three': 3, 'two': 5})
d
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# d['Three'] = 10
# d
# del d['three']
# d
# del d['Four']
# print(d.get('Four', 100000000000))
# d.get('Five', 'No such element')
d.setdefault('Five', 5)
d
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# for i in d:
#     print(i)
for k, v in d.items():
    print(k, v)
# print(list(d.keys()))
# print(d.values())
# for i, j in zip([1, 2, 4], [2, 4, 6]):
#     print(i, j)
for v, k in zip(d.values(), d.keys()):
    print(v, k)
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one 1 two 5 three 3 Five 5 1 one 5 two 3 three 5 Five

Set / Frozen Set

s = set()
# type(s)
s.add(1)
s.add(1)
# s
s.add(10)
s
s.remove(10)
s
# slis = [s, s]
# slis
# lisset = set([10, 9], 10)
# lisset
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geneSet = set([1, 2, 3, 6, 10])
geneSet2 = set([2, 4, 6, 8, 10])
geneSet & geneSet2
# geneSet | geneSet2
# geneSet - geneSet2
geneSet.intersection(geneSet2)
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Logical operators and control flows

  • Operators: == >= <= != < > and is not or

  • Branching: if ... elif...else

  • Loops: for, while

See also: Truth table

2 <= 3
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2 + 2 == 5
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'Z' > 'B'
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# Chaining is possible
1 < 2 < 3
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4 < 2 < 5
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(1 > 2) and (1 < 2)
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not 1 > 2
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1 > 2 or 1 < 2
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a = 1
b = 1
a is b
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a = 1
b = 1.0
a == b
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a is b
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if ... else

# if else elif. Note the colon.
if 3 > 5:
    print('Yes! It is true!')
else:
    print('No! It is not true')
    print('Inside of conditional !!!!')
print('Out of conditional')
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No! It is not true Inside of conditional !!!! Out of conditional 
a = 2 ** 3
if a % 2 == 0:
    print('Even')
else:
    print('Odd')
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Even 
score = 0
print("score =", score)
if score > 100 :
    print('What?')
elif 100 >= score > 80:
    print('Good')
elif 80 >= score > 60: 
    print('Okay')
else :
    print('Oops')
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score = 0 Oops

For loops

for i in range(2, 10):
    print(i, end = ' ')
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2 3 4 5 6 7 8 9 
for i in range(10):
    if (i == 3):
        break
    print(i, end = ' ')
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0 1 2

While loops

# while loop
x = 0
while x < 4:
    print(x)
    x += 1
    if (x == 3):
        break
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x = input('input a number')
while True:
    print(x)
    x = input('input a number')
    if x == '-1':
        break
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input a number 111 111 input a number 111 111 input a number -1

Useful functions

# print / input / type conversion / random / math 
# print(10000)
# print('Hello', 'world')
# print('Hello', 'world')
# print('Hello', 'world')
# print('Hello', 'world')
# print('Hello', 'world', sep = ' strange ')
# print('Hello', end = '\t')
print('world', end = '\t')
# print(end = '\n')
print('world')
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world world 
type(a)
# type(10)
# int(a) + int (b)
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# bool(0)
# bool(1)
# int(True)
int(False)
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# float(10)
int(10.9)
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import random
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random.random()
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random.randint(0, 100)
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random.uniform(0, 100)
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random.randrange(0, 101, 2)
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random.choice(['one', 'two', 'three'])
# random.sample((0, 1, 2), 2)
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import math
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math.ceil(9.1)
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math.floor(9.1)
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10 ** 0.5
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math.log(10)
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math.log10(10)
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math.exp(1)
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math.pi
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math.sin(math.pi / 2)
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math.cos(math.pi / 2)
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math.sqrt(10)
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File operations

  • open()

  • with ... as block

Runtimes (1)