5. Sequences: Strings,
Lists, and Files
Computer Concepts and Practice 2015 Spring
Practical Exercises
2015/03/25
Intelligent Data Systems Lab.
Seoul National University
String
An important data type in python
Supports many useful string operations
What we have learnt so far +, *, [], [:], len, for … in …, split
capitalize
find
isalpha
join
split
replace
upper
lower
count
strip
isdigit
index
https://docs.python.org/2/library/string.html
IDS Lab.
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String Operators (Examples)
Lower
Capitalize
Replace
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isalpha
strip
Join
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Practice 1: Palindrome
•
Examples
- Do geese see God?
- Was it Eliot's toilet I saw?
- Are we not drawn onward, we few, drawn onward to new era?
- Dennis and Edna sinned.
- Dennis, Nell, Edna, Eva, Dave, and Ellen sinned.
IDS Lab.
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컴퓨터의 개념 및 실습
B
e
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6
7
8
Practice 1: Palindrome
•
Examples
- Do geese see God?
- Was it Eliot's toilet I saw?
- Are we not drawn onward, we few, drawn onward to new era?
- Dennis and Edna sinned.
- Dennis, Nell, Edna, Eva, Dave, and Ellen sinned.
IDS Lab.
H
e
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l
o
0
1
2
3
4
5
컴퓨터의 개념 및 실습
B
e
H
6
7
8
Practice 1: Palindrome
•
Examples
- Do geese see God?
- Was it Eliot's toilet I saw?
- Are we not drawn onward, we few, drawn onward to new era?
- Dennis and Edna sinned.
- Dennis, Nell, Edna, Eva, Dave, and Ellen sinned.
IDS Lab.
H
e
l
l
o
0
1
2
3
4
5
컴퓨터의 개념 및 실습
B
e
H
6
7
8
Practice 1: Palindrome
•
Examples
- Do geese see God?
- Was it Eliot's toilet I saw?
- Are we not drawn onward, we few, drawn onward to new era?
- Dennis and Edna sinned.
- Dennis, Nell, Edna, Eva, Dave, and Ellen sinned.
IDS Lab.
H
e
l
l
o
0
1
2
3
4
5
컴퓨터의 개념 및 실습
l
e
H
6
7
8
Practice 1: Palindrome
•
Examples
- Do geese see God?
- Was it Eliot's toilet I saw?
- Are we not drawn onward, we few, drawn onward to new era?
- Dennis and Edna sinned.
- Dennis, Nell, Edna, Eva, Dave, and Ellen sinned.
IDS Lab.
H
e
l
l
o
0
1
2
3
4
5
컴퓨터의 개념 및 실습
l
e
H
6
7
8
Practice 1: Palindrome
•
Examples
- Do geese see God?
- Was it Eliot's toilet I saw?
- Are we not drawn onward, we few, drawn onward to new era?
- Dennis and Edna sinned.
- Dennis, Nell, Edna, Eva, Dave, and Ellen sinned.
IDS Lab.
H
e
l
l
o
0
1
2
3
4
5
컴퓨터의 개념 및 실습
l
e
H
6
7
8
ASCII Table
IDS Lab.
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String Formatting
Formatting Non-strings
<String> + str(<value>)
“<string>{0}<string>”.format(<value>)
“<string>%d/f/s<string>” % (<value>)
Formatting Rules
{<index>:<width>.<precision><type>}
<type> can be b, c, d, e, E, f, F, g, G, n, o, s, x, X, %
<type>
meaning
Example
e
Exponent form
2.34e+06
f
Fixed point
3.15
g
General
Both
n
General with locale
Both
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String Formatting
<type>
meaning
Example
b
binary
1101
c
character
'媿'
d
decimal
9832
o
octal
350
x
hex
e8
X
HEX
E8
s
string
Hello World
%
percentage
3.2%
You should at least remember f, d, x, s
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String Formatting (Examples)
Printing hh:mm:ss
Printing hex
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File I/O
Files must be closed after opened
<var> = open(“<filename>”, “<mode>”)
close(<var>)
You can omit close using ‘with’ statement
with open(“<filename>”, “<mode>”) as <var>
<statements>
….
File Modes depend on Operating System
For windows, “b” mode exists
“rb” = reading in binary mode
“wb” = writing in binary mode
The difference exists because of how line endings (\n, \r\n) work.
IDS Lab.
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File Modes
Mode Meaning
Pointer
Overwrite?
r
Reading only
At the beginning
No
r+
Reading and Writing
At the beginning
No
w
Writing only
At the beginning
Yes
w+
Reading and Writing
At the beginning
Yes
a
Appending
At the end
No
a+
Reading and Appending
At the end
No
rb
rb+
wb
wb+
Binaries.
ab
ab+
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Reading Lines
For <var> in <file>.readlines():
For <var> in <file>:
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Practice 2 Plotting Earthquakes
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